I've bought 8 or 9 blazers and about 5 suits on EBay. All have required at least some minimal alteration except two of the blazers that miraculously fit perfectly. In the end, it's totally worth the effort and the occasional trial and error -- how else can you get $4000 Brioni suits for $600? Or $2500 Oxxford cashmere blazers for $250? Etc. Etc. What's been said though is the mantra to follow: (i) know what the measurements are that you need -- shoulder width, chest width, sleeve length for jacket, total length for jacket in the back; waist and inseam length for slacks. Once you've got that nailed down it makes buying much, much easier. Also, it was suggested elsewhere to go into a Neiman Marcus or similar high-end store and try on various makes -- Brioni, Oxxford, Kiton, Isaia, etc. -- and then write down which size fits you best. (ii) stick to the top brands. Avoid brands that are known to be copied/faked, such as Armani. Also, beware of suits that consist of nice fabric, such as Zegna fabric or Loro Piana fabric, but are actually made by a no-name brand. (iii) stick to auctions with lots of good pictures. (iv) stick to sellers who respond promptly to email questions. (v) stick to sellers with excellent feedback ratings (i.e., 99%).