Questionable Client tries lure of "large white envelope filled with cash"

Does anyone know if “large white envelope filled with cash” is some sort of trope or an acceptable initial payment term? (Is it awkward to ask clients to NOT pay in cash? I use online banks anyway.)

There’s a potential client whom I’ve found questionable on many fronts that has tried to lure me into another in-person meeting with a “large white envelope filled with cash. That’s how we do things around here”. Unspecified – I’ve asked a few times for budget and high-level logistics and this client has strangely ignored the question.

This client has namedropped some large brand affiliations. I’ve experienced a surge in lower-paying gigs and a drop in the usual high-paying gigs I’m used to.

The project they want me to build is something that would have taken me less time than the wasted meeting time so far. (However, I usually charge a premium – it takes less time for me because it’s building on sourcebase I’ve already executed dozens of clients projects for)

• Meeting 1 went well, I think though was long – no time limit set per se since it was the last of the day.

• Remote Meeting 2 – they tried to loop a team in, and some technical issues with connectivity. I told them I can go right ahead and just build the app regardless of budget (some budget is nice though). They were supposed to provide assets and a project spec.

• Remote Meeting 3 – was able to talk to the remote team, and they were supposed to provide project spec and assets. They said they would and… not yet?

They now want yet another in-person meeting even though we agreed remote is fine. I’m a bit burnt because they don’t seem to have their act together. Also, cash envelopes is the way they do things around there? Are they the mafia?! For a junior dev, I am sure they would be excited, but the project for me is just a client project in a niche category of software that I’m extremely good/efficient at, but have absolutely no passion for – because I’ve done it so many times.

Aside: I’m starting to feel like I should just have a formal business team do this for me because I’ve effectively been selling the same thing to multiple clients (okay with customized branding, nuanced differences in UX/UI etc – the software looks different but it’s the same thing under the hood to me)

But the part of me that has been audited by the IRS wonders how dangerous is this “white envelope filled with cash lure” ?