Well, it depends on how you play your character but for 2/3 of my characters, money=training.

I suppose that's true...but still, a little persuasion (through bribery) and training isn't that expensive.

Funny part is, you can sell Daedric weapons and stuff for MORE than full price. Creeper and Mudcrab have their barter restricted, but you still have just shy of 1% leeway. In other words, sell a Glass Dagger worth 2000 Septims for 2019 Septims, if you care to squeeze every possible Septim out of the deal, like any self-respecting Imperial would do, while making it sound like you're cutting them a break.

Bribe merchant -> offer items up to 75% of the shopkeeper's maximum ->increase selling price to maximum ->keep clicking until the offer is accepted (dice roll FTW).
Same with buying items, take 25% off and click until accepted. I don't see it as exploit (then you might as well stop casting a spell or stop swinging your weapon after the first fail). I do avoid Creeper/Mudcrab. I always make potions and sell to Nalcarya, but even then I try not to exploit her item restocking (if you sell additional ingredients they will also respawn the next time - you could easily get her to own 1000 cliffracer plumes and trama roots ).