As a rule of thumb, I've found that when trading in, or selling, a commodity such as a handgun, you can expect the dealer to offer a price 35 to 40% lower than the retail price. In well over 35 years of collecting camera gear, that's generally what was always offered whenever I contemplated a trade. It's also the reason why I have several boxes in storage of older Nikon bodies and outdated lenses. It always seemed a bit foolish to get so little in return in comparison to what I originally payed. However, hindsight says that I was the fool, film cameras today have almost no value to anyone except a collector. What I should have done was trade them off while film was still being used.
As for firearms, the same deal applies and it does make some sense. While a markup of 35 to 40% may seem excessive, it's not once you consider the Cost of Money. That dealer may have to sit on that pristine model 29 for 2 years or more. This means that he has his money tied up in a commodity that doesn't generate any income at all until it's sold. Today, the smarter dealers use Gunbroker to get rid of stock that isn't selling. However, there are shipping and handling costs involved in doing this plus Gunbroker also gets their cut. Bottomline, if the dealer wants to continue to stay in business, he really doesn't have any option except to offer a wholesale price for your trade-in. BTW, on occasion I have seen dealers who will offer full retail on a trade, however in every case those dealers also are selling whatever you're trading for at a conserable markup compered to the dealers who only offer wholesale for a trade-in. Bottomline, if you trade something in, you'll end up paying the dealer the difference between wholesale and retail in one way or another.
Bottomline, you have 3 choices. One, keep that model 29 and just save until you can afford that new gun your lusting for. Two, sell the gun at retail yourself and risk getting a non payer or a scammer. Three, take your lumps and trade it in at what's been offered.