To what extent is it worthwhile to report check fraud / refund scams?

Places you could report this include:

• Your local police
• The bank on which the check was drawn
• The site on which you listed the car and were contacted by the scammer
• The phone company that owns the number you were given (if you can determine that, which you might well not be able to).

I'm not sure when you say "Is there any chance of prosecution", whether you mean prosecution of the scammer or prosecution of yourself. I would suggest that if you don't try to deposit the check yourself, the chances of you being prosecuted over this are exceedingly small, but that is purely my lay-person's opinion and IANAL. I don't think anyone can answer as to the likelihood of prosecution of the scammer.

Personally, I would start at the top of the list above and at least let them know; if they're not interested you haven't lost much (maybe a few minutes on the phone).

I largely agree with the answer from Vicky. I share the sentiments expressed in that answer and from another commenter about actual prosecution or stopping a fraudulent account; it just seems unlikely for anyone to move and if they do you won't even get a thank you email.

I would suggest an additional place to report it - your elected officials.

Write to your elected officials and share that you're a regular person trying to just sell a car. In your case you are even helping an elder navigate modern selling and advertising listings. This should be an utterly boring everyday event. Instead, a simple and mundane task puts you and your 90-year old friend at risk of theft, scams, and fraud. You have to go to extra lengths to protect yourself and even when you do see something fishy, you don't have any good avenue to report it to an entity that can take action.

Your legislators are the people who ought to be able to consider your interests and actually act on changes that make fraud harder or to put people who can stop it on the hook. If they cannot readily change laws or budgets, they can certainly magnify your voice.

You asked,

Who might care? Is it even worth my time to try and report this: is there any chance of prosecution?

Who might care is a bit of a broad question because it may differ from scenario to scenario. However, in general, there may be law enforcement parties who are interested. The US government maintains a website listing resources for reporting fraud and scams. Any time you are subject to a scam or fraud attempt, it's worth taking a few seconds to review that website to help you determine if, or how, to report the incident to the authorities.

However, you've raised another important possibility: Reporting to financial institutions.

Although this will vary in some fringe cases (Assuming no actual fraud has happened in a given case, Western Union is generally not interested in simply hearing that a fraudster asked you to use them, given the "popularity" of their services among scammers being a well-established fact), in general, if a fraud attempt is based on involvement of a given financial institution, they may be very interested in knowing about it.

Some scammers are dumb, and just randomly plan their attacks. No one worries about those scammers. But many scammers are smart. They will research their targets and attempt to exploit known loopholes. These scammers can cause significant losses - not only for consumers, but for financial institutions. Even when banking regulation essentially dictates that the victim should be left on the hook (i.e. for depositing a check that bounces), it's very often the case that the institution ends up at a loss anyways (good luck recovering thousands in losses from a customer who literally has no money). And, in some cases, regulation specifically leaves the institution on the hook (i.e. if the fraud is based on exploiting check endorsement requirements that the bank doesn't implement cleanly).

For instance, scams involving remote check deposit via a mobile banking app are often targeted based on known factors that a given institution uses when processing those checks. Some institutions only visually inspect checks that fail image verification when under a certain dollar amount, so scammers may try to exploit that by running fraudulent checks under that amount. A bank being targeted as such will have a critical interest in knowing about fraud attempts, because it can allow them to change their monitoring techniques to avoid being involved in fraud.

When a bank's anti-fraud team is evaluating data they have available with the intent of setting fraud controls, it can be a challenging balance between inconveniencing "good" customers vs catching the bad guys. But, even more difficult, with a purely data-centric approach, it can be hard to weed out actual, active fraud attempts from just plain careless or stupid customers behaving in a way that looks like fraud. For this reason, being alerted of an actual fraud attempt can make a difference.

Further, bank anti-fraud teams are often networked well with other institutions, and with law enforcement. One data point may not seem like much, but when people working behind the scenes to stop fraud are able to add that data point to a larger picture, it can make an impact. Receiving relevant, fresh information on fraud attempts can certainly lead to authorities being able to prosecute criminals.

So - to make a long story short - it may be the case that a bank doesn't care about your craigslist add. For a given scam report, they may not care at all. But it may also be the case that a fraud report can make a big difference, and they will care very much. For me, personally, that chance is worth spending a few minutes of my time by collecting the data I have and reporting it to any financial institutions involved.

The best way to do that may vary by institution. Some banks will have a fraud reporting mechanism on their website. Others may not, and you can always call their customer service number. Using specific fraud reporting tools that the institution makes available is probably the best route, if they exist, because run-of-the-mill customer service reps are sometimes thrown off by things that occur very infrequently (like, how to handle someone reporting a fraud attempt).

So the answer here is "The financial institution cares, and the FBI cares." maybe some other Law Enforcement organizations too. The Financial institution cares because if you cash that check just as the scammer asked and the account owner complains, the bank is likely out of money due to refunding the stolen cash. YOU probably won't get in trouble as you're basically a money mule/innocent dupe. At worst what would happen is you'd get an official "letter of admonishment" explaining your part in the fraud. Then if you do something similar the government can lay the hammer down on you because you were already officially notified about the illegality of your action. The FBI cares because it's their job to stop this sort of thing. Elder abuse/fraud/scamming is actually something of a priority for them. (https://www.fbi.gov/audio-repository/ftw-podcast-elder-fraud-awareness-061419.mp3/view) That being said the fraud/loss amount in this instance is really low, and probably under their investigative threshold. (an FBI agent working your $1500/$4000 case puts as much time in as one doing a $50,000 case.) But it's still good to report because it'll go "in the system." If you and 50 other people report that the same address/person/phone number is trying to scam them all out of $1,500 that's suddenly a $75,000 investigation. As to knowing if anything comes of it, possible but unlikely. You lost no money, so obviously you can't get any restitution. But you might end up being interviewed, especially if your report pushes the crime over the line of investigatory interest. Even if you get interviewed though you'll almost certainly never know what comes of the case, unless you put up a Google Alert for the scammer's name and find a news article about it after they're convicted.

TLDR: Yes the government cares. Report it to the FBI. It might get prosecuted but you will almost certainly never find that out.