Seconded. I never contribute to sales discussions on here but feel compelled to comment here.
FYI - I portfolio invest and have no 20+ unit positions & therefore my experience may not represent yours...
I sold off all my "big set" inventory - EEE, HH, EV, Tumblers, GE, TH, PS, GC plus some one-off big sets like SSD and SOH [and a bunch of mea culpa Orthanc and Death Star losses] - over the last 2 years. All FBA.
My returns have been on the smaller <$100 minifig-centric sets I sold, never on the big ones with the big exceptions being a MF and a few $$ 1st series Friends sets.
Against total sales volume my losses have occurred at amazing breakage % (< 1%).
YMMV