Some years back, I spoke to a gunshop owner specifically about firearm resale. I felt the time was ripe for firearms investment ... the short answer is that you will need to select your product (rifle, pistol, shotgun)your personality 'market' (how they buy, how much) and type of artistic level each category represents.
On shotguns, old world craftsmanship combined with real engraving will drive prices high as long as you are able to persuasively explain the history and features. A basic Churchill shotgun may fetch 2-3 grand in plain-jane finish then in the thousands if engraved. I sure you have seem 50k shotguns but do they sell, is there a buyer. An old Damascus side by side with proofed barrels is out there but who will want one.
Rifles seem a little easier as the year cutoff will determine worth. Pre-64 Winchesters are slowly climbing but may be not different than inflation. Buy a real Rigby with history and a few years from now it could bring in 20-25k. An original commercial Mauser can offer great value especially if the version is the right caliber.
At this same shop, 2 real Rigby' arrived, one in 7x57, and were displayed next to the original 7x57 Rigby Bell used in Africa (on loan from Rigby only!) The new 7x57 was $12k, the original nearly priceless - to gun history enthusiasts.
Pistols are their own animal though craftsmanship combined with vintage all have to meet and stars align.
The point is you will need to select the specialty you want and buy wisely. Invest the time to know what is of real value and what is a passing fad. I would suggest watching selling sites and understand what actually sells rather than what is listed.
With the economy the way it is, the next 6-9 months may be the best buying period ever. Good luck - tell us what ya get!