It depends how much you have spent if you spent over 50k I think it’s not wrong to assume you will get offer from shop B with a bit more spending.
Two approaches
1. You can talk to shop A again and told her it’s a mistake and you want to stick with their shop to continue to spend. May be hinting you can buy a bit more if they can give you the bag right away
2. If they refuse then you can go to shop b and tell them this story and if they check your record I think they will want to have you as their client as you keep spending. You should hint that you don’t mind to switch over due to this very bad experience but you want to get offer faster as it’s a total loss at shop A. I had that experience before and they would get special approval for manager if they value you as a good client