That’s a good point. My thoughts are you shouldn’t be left in the lurch when your AD loses the relationship. You should be invited to shop at the nearest AD and your interest list and purchased piece history should carry over to the next. Like with Ferrari or Porsche etc you’re not just left hanging once a dealership closed surely?
Regarding selling pieces, like car analogy again you should be able to trade in a mid tier complication with your AD and buy a new grand complication. There is nothing wrong with upgrading your timepieces and can’t be expected to keep everything as sometimes a piece does not click for you. Take the piece back in from your customer have a certified pre owned with the AD and reward their loyalty.