As a submissive and a student of psychology I would have to say "bribing" your sub to do something is one of the worst things you can do.
A sub should want to do something for their Dom because of the way it makes them feel knowing they gave pleasure to their Dom -- that's part of the role. This reward should strictly be the warm cozy intrinsic feeling of "I'm a good sub because i made my Dom happy". I don't agree that children should be bribed with money for good grades or TV for finishing their dinner. This only teaches them to do these things because of the "material reward" and gets too far away from the real reasons they should be doing these things. Same principle for a submissive. We do things and behave in ways that please our Dom's -- that in itself is the reward. To me this is what being a sub is all about. I am rewarded by the way my Dom looks at me, holds me, kisses me, etc when I've done something for him or to please him -- it's why aftercare exists. If i endured an especially difficult scene, being rewarded with a bubble bath, romantic dinner or something of the sorts afterwards may be a nice perk - but i would never want to enter a scene with that as a thought in my head and getting those things has to be "special" not something i expect after every scene.

This may have something do with how i see punishment. Yes, i can enjoy pain but i am not a sub that seeks out punishments just to get spanked -- if i want that, I'll ask for it. I also don't believe in a punishment having to happened because i did something wrong. The thought that i brought displeasure or disappointment or anything of the sorts to my Dom is a more miserable experience than anything he could dish out to me. I see punishment as a way for us to move past it together -- he acknowledges that I've done something wrong and the action of the punishment is more so taking that guilt and worry away from me, because i know when the punishment is over, he's forgiven me therefore, i can forgive myself and together we can move past it and forget about it.