You can look at completed listings for a category or description, which will show you sold prices over the last month but it could be that no bags exactly the same have sold. But it will give an indication of the sorts of things that sold and how much they sold for.
What I normally do is look at an item -eg a bag, from several different sellers. I type in what I am looking for and see what comes up.
Look closely at the photos.
Read the description very carefully.
Especially where it gives sizes or quantities.
Be careful of buying from overseas.
If a brand name item is advertised as brand new and is a quarter the price of the real thing, be very wary.
It's pretty much like being at the shops, you just have to make a decision based on price and what sort of quality you think it looks to be.
It's second hand items where prices can vary wildly, I find.
