Howard that is bit of a blanket statement #3, I hope it was tongue in cheek.

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We always chuck puzzles that say I piece missing, we can only sell what we are given. I have done 2 x 500 this weekend, only one is going back to the shop.
I am sure that most are happy to take a chance when they only have to pay £1 for a puzzle as opposed to around £7 for a top quality Ravensburg or Falcon puzzle. We have a high turnover in puzzles for that very reason.