If I told you then I couldnt sell the book!
Really this subject as a whole in general. There are always going to be people that think they should get retail price on a trade-in, but for the most part as long you are reasonable with people or at the very least upfront with why you giving them what you are there are situations like this can be avoided.
You are the vast majority of the time going to get more money from individual than a retail business. Just apparently some retail business's are a little more reasonable than others. Course we dont know the entire story, so its hard to say.
Edit: I'm also not insinuating that G&L is better than whomever else. There are some shops that just have to have a higher margin in firearms due to overhead. Every business is different in that regard - thus why we have the luxury in this country of shopping around.
Edit x2: Also consider that you pay taxes on the difference of a trade, so you are getting a little more than face trade-in value in that regard. A $800 tradein would actually be also saving you an additional $78 in sales tax.