I've never asked for or expected any compensation for teaching R/C, but I have accepted a cold can of pop or a few bucks as a tip. But my favorite was when a friend of mine and I were taking turns instructing a guy who had moved here from Korea. We each got him up for 2 or 3 flights, then he thanked us, packed up his plane and left. About 30 minutes later we saw him drive back into the parking lot and thought 'What's going on? Did he forget something?' He brought back a bucket of chicken and a six-pack of beer! What a guy!