The issue with declared MWT's at UK auctions is a big one. There is one well known auction house in the UK whose MWT's are often very 'generous' and another that is often quite pessimistic, definitely erring on the side of caution. Ever since being caught out by the former, I try to NEVER buy at auction without measuring the MWT's myself or by a trusted independent.
If for some reason I HAVE to bid on a gun uninspected, I allow for a 10% 'generosity' in the supplied figures, prepare myself for an unpleasant shock and bid cautiously. Thankfully, in recent times this policy has saved me from too many heart stopping moments!
I think it is important to bear in mind that although some lots will have come deceased estates etc and be genuine opportunities, many will be being offloaded by the trade who just want to see the back of a stock item with issues that can not economically be fixed.
In fairness, it should be remembered that the UK gun auction system was developed to sell guns to the guntrade, not the public, but with the internet has become considered an almost a retail environment. The result is that the innocent are buying guns at 'fantastic' prices without the knowledge to know a 'pig in a poke' from a 'bargain'. You can't blame the auction houses for enjoying this new(ish) market sector and their only legal obligation is to the Proof Laws which themselves leave a lot to be desired.