If you have to go this route, be sure to meet that client in a public place.
They invest in feet pics for sale so that they can profit from it in some way, and in turn you earn when you sell foot pics to them.
You can sell feet pics on Facebook by joining existing groups with buyers and sellers or even by creating your own group.
Think of a foot model routine as preventative maintenance.
Especially when your ideal audience are those who care more about other parts of your body than your face.
Thus, if you are creative enough, such websites are your go-to.