You might think so ... That the seller is at liberty to accept or reject. .. There was is an interesting case in northern Ireland, within the current year , where a family bakery were taken to court by persons representing a marriage equality agenda ( same sex marriage) for refusing to ice a cake with slogans promoting this agenda. The bakery is was run by a family with strong religious convictions regarding the sanctity of traditional unions.As I said, he sold me my battery - at a small discount - as a first time customer.
No business is obliged to deal with anyone.
To use the quaint legal phrase, an offer of something for sale is an 'invitation to treat'.
Strictly speaking, when you buy anything you make an offer to the seller who is at liberty to accept it, negotiate with you, or simply refuse your offer.
For the vast majority of transactions the process is streamlined, you offer the advertised price and the retailer automatically accepts it.
But it doesn't have to be that way.
The bakery lost this case and the subsequent appeals