Dies to Removal

I don't tell them what the cards are worth, I just find something I want and go "I want this." I let them pick what they think is appropriate and if they're happy I'm happy. I don't feel bad about it, it isn't my job to tell you what your cards are worth, and worth is in the eye of the beholder anyway.

It isn't sharking, you offer person a card for their card and they say ok. You did nothing wrong the agreed to it, they wanted to make the trade

When you take advantage of the fact that one party does not know card prices and leverage their lack of knowledge against your knowledge, which I assume is what you mean by "offer person a card for their card and they say ok" that is the literal definition of sharking.

nValue is subjective though. There are a lot of different levels of players. Finding casuals that are simply interested in bulk rares shouldn't make you feel bad, especially if you're giving them the better part of a new deck they're working on.

Example: There's a store near my house that is mostly board and tabletop games, not really big into CCGs. They have some people there who play Magic pretty casually. One day I showed up with my bulk box and found these two guys who were working on some bad tribal decks (sphinx and cats I think?) so the bulk box, to them at least, was a goldmine. I traded one guy like 12 bulk rare sphinx's for a foil Boros Reckoner, and the other guy I traded a set of Door of Destinies for a Dark Confidant. Was it a balanced trade? Clearly not. But those guys got what they wanted, and the value of not having to find these "cool" cards on their own outweighed monetary value. Everyone in all parties is going to actually play with those cards, so no bad feels.
(Although I have yet to find the last Bob I need, so...not quite yet.)