Ho Sammieg, welcome.
I buy and sell on
ebay and there are always going to be people who try to sell things that aren't the best for more than they are worth.
Look at the feedback and look at the pictures and then ask for better pictures and explanations of anything that you are concerned about. You can find out a lot about sellers by how they usually answer they mail.
Don't think that everything is going to be perfect when sold as that is why there are premiums on the better stamps. Most stamps are not perfect. But, that is OK for me as I am not either.

The catalog prices are just what dealers are selling really good versions of the stamps for at that time.
ebay prices will usually be less than catalog and depending on condition also.
Some sellers call a stamp very fine, for example, but when I look at it it looks like Fine or Very good and not all sellers disclose the flaws or faults of a stamp (which they really should I think). Sometimes people male mistakes, and a good seller would admit his mistake and refund your money and apologize.
Do not assume that the words that are describing the stamp(s) are accurate. They may be, only to the sellers standards, which may be lesser than yours.
Photos / scans of stamps. Maybe your library has a scanner and you can log on to one of their computers and use the scanner and either take it home and edit and crop it and resize it or do all that there. My library has better software on their computers than I do.