I think it's fine to allow it but if you're going to price things based on the individual buyer, you then should be forced to accept counter offers. Make everything negotiable.
$5.00 for a gallon of milk? No, I'll give you $2.50. Back and forth until you find a mutually agreeable price.
What happens if there's no agreement, you either walk away or concede to buy at lowest offered price? Seems like the store's AI should stick to its guns every time if you're already in the store.
$5.00 for a gallon of milk? No, I'll give you $2.50. Back and forth until you find a mutually agreeable price.