The employee behavior you received makes me simmer with frustration; it would not have been tolerated in my former shop.
That being said, though, with your comment about the clerk needing help from another employee to complete your transaction and board recommendations for the shop, I wonder if it's possible the shop was under-staffed or temporarily staffed due to other employees/owner being at a show somewhere. Sometimes it's hard to manage things as an owner when you are spread over two or more locations for the week/weekend.
I'm certainly not excusing them; just wondering (kind of hoping?) if there were extenuating circumstances this time.
Jan in VA