"Eg if I owned 1000 of AUM at $12, say I put them for sale at $100.
TDWaterhouse would not accept that order - too far from current market price."
Perhaps TD wants to short without incumberances?
Even if you do place your shares for sale at 10x+ their current price, every investor would have to do also to be an impediment to shorting. That never happens, so it is a lost cause.
Unfortunately only thing that will stop it are enforced regulations agains such. Fat chance.
Ed.