Please don't bring your basket here

Last week I dropped into a local supermarket (Tesco) to pick up literally a few things. I took a basket, selected my items and went to a checkout. The checkout was completely clear and the assistant, an older lady, was sitting waiting for custom. I took my basket to her and started to unload the few items (3 or 4 only). She told me that I should use the basket checkout down at the other end of the store (where there was a queue) as her checkout was only for trolleys. I said that I was surprised and was this a new policy. She said no, just her preference. I asked her would she prefer that I spoke to her supervisor as I felt that if individual assistants are gong to make store policy, then the customers should know, so that we could prepare ourselves perhaps by shopping elsewhere. She served me, but with very bad grace. Do your store assistants sometimes grumble abut you?