Hi Sculpin, in many years trading, I've only been asked to loan shares for a fee, twice, and I assume, that's because I'm not usually holding enough to be of interest to the pro's.
On both occasions, I have declined the offer, however I have absolutely no way of knowing whether my shares were loaned or not. Had I immediately put in an order to sell those shares, at or near matket price, then I just become one of the many sellers. The only difference is, I'm selling something I own but the 'shorter' will sooner or later, have to buy.
So, ...............I don't know if/when my shares are being loaned to manipulate against me. But I can assure you, no ones paying me a rental fee.
Sorry I can't be more helpul on this subject, if we have a professional shorter or broker on board, maybe they can tell us how it really works.