This is such a useful thread, and with that in mind, I thought I'd 'give back' because you ladies have helped me make great eBay purchases! I've got a few to add, and reaffirm, on this topic.
GOOD eBAY SELLERS who ship well-packaged items quickly:
my-boo-kitty (Popular US seller. I just bought my first MAC item from her - a LE Studio Finish concealer palette w/ SPF 35 - am thrilled with it! Incredibly well-wrapped so it arrived in perfect condition in the post.)
lynnandjason1998 (Another good US Seller. I bought a 187se from them, and I'm very pleased with it. Arrived well packaged and came quickly.)
katya_127 (UK Seller. I bought the MAC formal black ruffle with 5 short-handled eye brushes. Arrived quickly and wasn't too expensive, and came with freebie samples of perfume and shower gel.)
xbeautylisciousx (UK seller. Bought glitz & blitz fluidline from her, and it arrived very quickly and was very well packaged. Not bad prices either! She has a lot of NARS brushes up for sale right now.
eBay sellers that I'm waiting on, and would welcome any thoughts on:
makeupmaniacs (US Seller. Bought 2 mixing mediums, an eyeliner and a face & body, on 12 May - seller says it was posted on 15 May - and I'm still waiting for it to arrive. It was international post, so I'm not seeing it as a delay - yet.)
samphora-face-treat (US seller who sells mostly pressed pigments. If you buy 4, she gives a complementary e.l.f quad, and if you buy 15, she gives a 15-pan-slot MAC kit. I've bought 15 today and I'll update when I get it. She has to send it internationally to me, so it'll be a good test of how well she wraps it.)
awful sellers to avoid at all costs:
swoosh_uk (Got a separate thread on that, so I won't repeat it here.)
Thanks ladies!