I buy stuff on eBay. I can't be bothered with browsing, so I will normally search for a specific item eg marks and Spencer bra and then filter by size and condition.
My recent purchases
BNIB kurt Geiger boots £200 (allegedly) down to £40. This was just a browse of KG footwear in my size, but I have had loads of compliments on them already.
BNWT Fat face dress £50 down to £25. Clothes can be tricky unless you are sure of your size and how it will look. This dress was a style I know suits me and it was a wrap dress made of jersey material, so I knew i could adjust it to fit.
Miller Harris perfume - really wanted a bottle of a particular perfume but was £100 in the shops. I found an BNIB bottle for £50. There are a lot of fakes on eBay, but MH is a niche brand, so much less likely to be faked than say Chanel. The seller had good feedback and a long history on eBay.
My tips:
Start small - I was nervous when I first started buying on eBay, so I only spent what I could afford to write off. If I have had any problems, I have been refunded quickly.
Check the sellers history and feedback - I have a quick scan of the ratings, location and listing itself. If I feel anything is 'off' I won't buy from that seller.
Be aware of sellers overseas - I have had some great non-S&B bargains, but stuff from China takes ages to arrive and I'm always conceded about returning an item if there is a problem, so I don't buy anything I'm not 100% sure of.
Beware of fakes - if a deal is too good to be true, it normally is. I wouldn't