Read their ads, do searches on on TER, read reviews, ask other hobbyists.

If they post a lot of photos of their feet on their site, the chances are good that they are into it.

Is it even illegal to pay someone to rub and kiss their feet? It shouldn't be, but of course none of this stuff should be illegal between consenting adults.

Those are good ways but I do it yet lol most don't come for that.

also read their FAQs on their site. Many will say they do fetish sessions or something of the like,  then just ask. I love including foot fetish stuff in sessions and i know im not the only one!

xoxo
Jenny

some state somewhere with laws so broadly drawn that you can't even touch another person if there is any exchange of money.

The problem may come up if this contact is described as massage because most states have laws pertaining to licensing of massage and any violation of those laws could be a felony in those states (for example, mine:  Massachusetts.)

Of course, there can be no genital/foot contact or that will be considered prositution, I'm sure.

(still not a lawyer)