Sure

Replying with a simple "sure" might come across as impolite. In a retail store, I would recommend that you tell the sales assistant what you're looking for. Likewise, with other types of businesses you should state the purpose of your call or visit.

‘Sure’ has the suggestion that the other person is benefitting from the interaction, not you. That’s not usual because the default in a store is that the person is there to help you. Oddly you can answer both ‘Yes, please.’ and ‘Yes, thank you.’ There could be a situation, however, where a lot of people are competing for your business and they will benefit from it. In that case ‘Sure’ might be a good answer. It would be as if ‘Can I help you?’ really meant ‘Can I try to sell you something?’