Say I have a character that is an adventurer, through and through. He doesn't seek to amass or collect powerful relics or ancient artifacts. He wants to profit from their sale!

My question is, from an RP standpoint, who are the best people/traders/shopkeepers/scholars to give these artifacts to? I mean sure, I can sell generic ABC item of generic XYZ enchantment to just any old merchant. But things like daedric artifacts or other unique/legendary items? For example, I can take rare and valuable tomes to Urag at The College, or any Dwemer artifacts to Calcelmo in Markarth.

Hmm, that's a good question. Usually I collect all those things and leave them in my house.

There aren't too many specific merchants that would be interested in those things, lore wise. I would say either professors at the college so they could research and care for it, or maybe like a jarl's wizard... someone in authority. Maybe sell something to a fence down in the Ratway if you can justify why the TG would be interested in it... like maybe the Masque of Clavicus Vile because they would be interested in the Persuasion and Barter enchantments, or maybe the Aetherial crown just because it's a valuable old crown.

Can't remember, does anyone in the Dark Brotherhood buy/sell? If so, they would surely be interested in Mehrunes Razor.

Use your imagination.