With almost every new game with micro-transactions I see people upset that certain items are cash-shop only. I've seen the worry of cash shops ruin tons of games before they are even played. And if you think a "cosmetics only" cash shop has any sort of profitability u are sorely mistaken. It only works in games where looking good is the goal, and there aren't many of those types of games.

What exactly is acceptable to sell? (giving that the pricing is also fair)

For my experience these are the cash shop items I approve and disapprove of:

Lock boxes
Cosmetic options
Skill resets depending on the game
Bank/storage/inventory space
Premium pets/creatures/mounts assuming normal ones can get gotten in-game
Resurrection scrolls
Experience boosts

Pets/creatures/mounts that can only be obtained through cash shop
Anything skill related
Endgame gear
Gear protection that's guaranteed to protect something when upgrading/reinforcing
Stat/damage boosts