As others mentioned, whatever you do get it in writing. I've seen several deals start out good and go south in a hurry when people don't agree on things.

As for the ehtical side of things, the SOP's I've seen just address inspecting a house for someone else that you might have an interest in. I've always thought this is to stop you from talking some buyers out of buying just so you (or someone else you know) could.

It seems like most of the rules and laws surrounding this stuff are about disclosure of some type. I've just always been up front with sellers and/or their agents about what I do for a living so nobody can say I was being deceptive.