It's Sam here...there are 2 main types of wtb post:

1. Items you cant find anywhere - they may be rare or in limited quantities such as a pair of Nike Air Mag sneakers. In this case you'll be better placed to find your ideal product.

2. When you don't know exactly what product you want - people create 'want to buys' for generic items e.g. 'a black trucker hat'. This way, wtb posts can actually aid product discovery and make the whole shopping experience easier and less effort since sellers are coming to you and not the other way round!

Thanks!