They are better for the young end as so many people buy new before they have kids, and get given 0-6 month clothing as gifts. I help at our sale so I can presale shop and have to loiter near the boy stuff as it is being put out to get the best stuff for Seb (i.e lots of cheap trousers and shorts in the hope that we'll be potty training), whereas there was so much girl stuff for Anna that the rails were jammed making it difficult to get things off.
It may sound snobby, but if you can pick a sale in an affluent area, the stuff is generally of better quality.
Don't get carried away and be wary of buying too much that is packaged in freezer bags (e.g. vests, bedding) as it may not turn out to be as soft as you'd hoped for, plus sleepsuits etc will have shrunk in the wash & reusable swim nappies may be somewhat stretched around the thighs.
For things like front carriers, pushchairs make sure you know what brands/models you'd consider before going. We bought a 2nd hand front carrier for Seb and it wasn't comfortable so bought another one new for Anna. For things like baby baths though you can see what you're getting and can't really go wrong.
Get there on time to queue (& park), have a list of what you need, don't have bags or a pushchair with you if possible, and cheque or cash to pay (although our sale experimented with chip and pin last time).
Overall you should get bargains but expect to end up with a couple of duff items...
Enjoy!