Bribery? Exploitation? Coercion?

Is training dogs exploitative? Is it, in a positive framework,  simply a matter of bribery?

No
and another no.

Google suggests that synonyms for exploitation include: abuse, dishonest, profiteering, using and many other unpleasant terms all suggesting a one way benefit.  Bribery's list is nearly as bad:  exaction, extortion, milking, payoff, ransom etc..

Training, at least around here, is a two way street. We all benefit from it. We all, at least generally, enjoy it. The dogs want to play work. They ask  for the opportunity to train - frequently and with happiness. There is an ex-pen set up on the lawn .. every dog will randomly hop in just to see if they can get a session going.

It's hard to play with just one dog as everybody wants in on the action. 

The specific topic of bribery came up recently when Sally and I took a moment out at a social function to do some work ... she spun, and wove through my legs, did her head thing, hammered my hand with her nose touch  and was happy happy to be working. When we were done and starting to wind down I paid her with a bit of a treat in my pocket. Someone who had walked up said "I knew it was all bribery!" with great glee. I got into the whole pay for performance thing - and showed him luring vs paying. He got it. Or at least he was polite enough to say he got it!