Could you tell me the difference between big and small shops in their service?

Most places nowadays small shops try to imitate larger shops in service as best they can so as to attract customers. They have much more forgiving return policies and such for this reason.

In my experience, smaller shop employees are likely to be more friendly, as it more of a friendly environment. At Wal-Mart, the people there... don't want to be there, so they don't talk to the customers and just do their job (except for the people who work the video game areas, they are generally pleased with their position), whereas Kroger has nice talkative people even though it's rather big.