But they have not only managed to prevent silver pushing, they have also managed to deter ordinary people who use auctions regularly (like myself) from bidding on items. They should really have thought harder about the situation - there are many ways to do it. You suggested a good one.
I do remember, now, the master builder costing 1g. Apologies. But again, if you use the master builder far more than 50 times, then the 50g price for unlocking is worth it (and possibly the subsequent 75g for the next unlock), but if not, it is again unfair.
I imagine this is all a trial, anyway, to try and perfect the systems they use.