I would move this thread to the eBay section but Topaz won't then be able to see it as they aren't a VIP member.
What I would say is in my experience it can work well but I would:
1) Only sell items that are worth a decent return - say above £10 - for me as an occasional seller it's not worth the hassle of photographing, packaging, trips to the PO etc without a decent return.
2) Fees for eBay and Paypal will eat into any profit you make so consider start prices for your items carefully, they need to be low enough to attract bids but high enough to cover your fees and the effort of selling.
3) Always use recorded delivery - now the new rules are in where sellers can't leave negs, buyers seem to be getting pretty savvy that they can claim 'item not received' via Paypal, Paypal will always find in their favour and return their cash unless a seller can prove the item was received (ie recorded delivery) and the seller can't even -ve feedback in return even if they know they have been duped. Just wrong IMO
4) Unless you have oodles of time, don't sell too much in one go because the admin time spent in organising, packing and posting is more than you would think.
Other people who sell more can probably give you better advice but I stick to these things when I use eBay.
I hope I haven't put you off - eBay can be a great tool and a useful way to make some money