I've noticed a few things about consignment, just to add.
(1) The guy selling the gun is usually older, not willing to deal with technology or shipping, and is trying to unload something. Sometimes they're commodity guns (I bought a 930 JM Pro through consignment), sometimes they're weird - one of my local FFLs recently posted a Romanian pre-Century PSL for sale that he got in on consignment. Some FFLs keep consignment guns on the wall and basically treat them like their inventory. Others list them on Gunbroker because they know some weird antique or C&R or whatever simply isn't going to sell quickly, which leads me to...
(2) Consignment also tends to show up often when FFLs have a hard time getting guns. This has been pretty common since last year. FFLs need a stream of cash to keep going and consignment guns provide that when new inventory is months, if not years, away. I've also seen it with new, smalltime full-retail FFLs, like a FFL whose new to the scene but doesn't have the cash to buy a full inventory of guns.
(3) Consignment makes trades and haggling complicated for a potential buyer because the shop handling the consignment is supposed to take in X amount of cash. I tend to know my go-to FFLs fairly well, so I know what their profit margins are and I know how much room I have to haggle. Especially with something that's quirky or needs work. Consequently, I've seen consignment guns sit and sit and sit for years because the sellers set unrealistic price points, the shops don't explain this to the sellers, and there's never a deal made to get the gun to sell at a reasonable price for all involved. Basically same thing as on here where a gun sits for a year plus.
(4) There's also consignment through auction houses, but that's another topic for another thread.