How we distinguished charges and named them?

As I searched history of nomenclature of charges I got this..,

Ben Franklin imagined electricity as a type of invisible fluid that could build up or be absent from a material, or at least certain materials. He believed that when this invisible fluid built up the object was positively charged. When there was an absence of this fluid he called that material negatively charged.

Benjamin Franklin thought of electricity as a fluid, and said when there is abundance of fluid it is positive, stating positively charged fluid flows in electricity.

Further, Thomson found that negatively charged particles flow and not positive ones, as the cathode rays exhibited characteristics of negatively charged particles. But how we first clarified what is what?

How we distinguished between two types of charges and established their properties? Positive charges repel positive charges and attract negative ones. But from there we can’t say whether the particle we are trying to understand is positive or negative. So how Thomson said electricity is flow of negative charges?