I love bookstores - any bookstores - and when I go into them, I find there's a few things I expect to find in them to make them the types of places I'd come back to.
Variety is the spice of life. And so it is the same with bookstores. You gotta be able to walk into a bookstore and find exactly what you're looking for; be it sports, non-fiction, cookbooks, textbooks from the past, world atlas' or chick lit, you have to be able to find what you're into in any bookstore you venture into. If you can't find everything you want, the owner isn't doing you - or the public - any favours.
Light and Smell have always gotten a way to either bother me or keep me looking around. If the place isn't well-lit, I'm not going to bother going back to it. Some bookstores have plenty of old-fashioned lamps here and there - all in use - to give the place character and that homy feeling where you don't want to leave. And that's great! However, if there's a doorway into a room and that room has no light in it (or no source where you can use a light or a torch in some way), you're not going be enticed back to the store again, are you?
And with smells? There's nothing worse than a bookstore that has that mouldy smell about it. It says that the place leaks - or the air-conditioning does - and that some of its carpets aren't cared for and books will have absorbed that smell too. Now, you're not going to want to take home a book with that smell and add it to your collection; are you? I have also ventured into a bookstore where all I did was sneeze. The place was so dusty that the further I ventured in, the worse the dust was - and the place was a great bookstore! I wanted to go back but how could I when I ended up using up all my tissues before picking out a book?
Ordering in. If you can't order in a book from outside, it's not worth it. This means, the store owner doesn't talk to other second-hand bookstores and doesn't have the net hooked up. Or if they do, they don't know how to use it.
Toilets. I hate to say this, but some bookstores are situated nowhere near public toilets; and I have found it a great relief when I have needed to use the Ladies and found the bookstore I'm in has one at the back of the store. And what surprised me more was how clean it was kept! I have come across some places in the city where if you want to go to the toilet, you have run across the street, into another building, to the top floor and use the only ladies toilets... this is not a good look and has happened to me once. I haven't been back to that bookstore in the city for that reason.
Layby. If you can't do this, forget going back. You're going to make the effort to go to their store to pay off something they are going to hang onto for you. It's an insult to you if they say no.
Coffee Shop. If there's none instore, the owner should know where there's one nearby; a good one too. The coffee shop shouldn't be more than two blocks from where their store is and shouldn't be too expensive to have something to eat there either; no matter what the place looks like, you can have a great coffee in the most interesting places.