The suggestion that you contact Ian Boulton is a great starting point. He's a straight shooter and his auction fees are less than most.
If you have an item (any item) that is offered with neither the seller or the buyer acting under duress with the item correctly described, properly advertised you will end up getting the true value.
The problem any seller has with no background to the money expended on the collection or the current state if the market or knowledge of the subject matter, there is always a tendency to think they are being ripped off.
It looks like a reasonable collection, put together with some expenditure and consideration. If you have any of the stamps in the attached images, they are what I collect and I would make you a fair offer for them.
Another consideration is condition. A stamp that is well centred within the perforations and in the condition it would have been on the day it was sold will be worth many times more than the same stamp that is off centre and has discolouration or damage.

