and a note: i tried a GetAll() scan from TradeSkillMaster, it behaves the same way as Auctioneer.. it displays the full AH in a single huge list for a few seconds.
all AH addons that use the GetAll() Blizzard API will do this - it's standard Blizzard API behaviour for this function - maybe add a hook to it and disable the overlay while the scan is running?
p.s. for the tiny frame there's a solution: disable CompactUI option in Auctioneer settings. I run Auctioneer with CompactUI disabled and it uses normal item icons. CanIMogIt icons in AH were looking just fine in 7.3.0.03 for me.
It's only a problem if you have CompactUI enabled in Auctioneer.
To disable it: Auctioneer configuration -> Util modules -> CompactUI -> disable the checkbox for 'Enable use of CompactUI'
and then /reload the interface