If there's a man at the behind the counter then theres no way you can help that can you? As long as you enter the shop with the intention of just getting your stuff and leaving. But if i saw that there is only one man behind the counter, and i'll be the only one in the shop with him, I'll leave. You dont know what could happen.

Also the Sahabah used to do business, sell goods, and i'm sure when you sell you dont sell to women only or women only. Mixing here means without a solid reason, just for fun, just for chat, or oh i didnt see him for soooo long and we used to be co workers yadda yadda. It'll be better if you can avoid mixing totally though. But some times its just not possible i guess..like on the bus..lol.