Welcome bazzbozz.
When you look at
ebay or BidStart or DelCampe you have to look at the prices things sold for, not the prices some people are asking, to get a true value.
Someone selling has to make a profit of some sort to keep selling, unless he is just clearing house. And when you are selling, you will not get the price they are asking. 10% - 25% maybe, maybe more if they have a buyer for that kind of item. The more stamps, the less you get for each item.
There are bargains to be had of course, just be patient. And the more time and effort you put into selling something the better your sales will be.