For sensored motors it is easy, just look at how many turns the motor is rated at, and how many the esc is rated for. Just don't exceed this. For others though, it can be harder. I. Think it comes down to common sense. The problem is, it is hard to go off of amp rating as well. The mmp is only rated for 65 amps con, yet people use those in 1/8 scale cars.

There is not a set in stone way though.