Is it ok to go to a seforim store to look up something very quickly in a sefer, to clarify something that I’m learning, or is that gezel? I wouldn’t otherwise buy the sefer for this one-off thing that I need to look up.
The answer to your question really depends on the owner of the seforim store, if he indeed minds then it is not permitted, but if he doesn’t then it is. As a side point I know of a seforim store that allows people to look in seforim for up to 5 minutes. Therefore the best things is to ask the owner of the store.