I have a lot of valuable loot that I collect in Skyrim. I have no need for most of it, and would like to sell it off, but it's hard to find a merchant that will buy all the random loot I've collected. How do I find a trader that will buy all my valuable loot?
In most cities, there's a number of merchants who will buy various different wares from you which are comparable in kind to the ones they sell. And most cities and towns have at least one "general goods" merchant who will pretty much buy anything. In Whiterun, you'll want to visit Belethor's General Goods.
For stolen merchandise, you'll need to find a fence. The earliest one you'll probably have access to is Tonilia, in the Ragged Flagon under Riften.
The main limitation you'll run into here is that most merchants only keep 500-750 gp on hand, and fences start at around 1k. So, if you empty their bank by selling too much to them, you'll need to wait a couple days before they have the funds to buy more from you. There's a few perks and other workarounds that can be used to deal with this.
Also, be aware that most stores are only open from 0800-2000. If you're trying to sell your wares at night or early morning, you'll probably have to wait.
I strongly recommend you search this site for other skyrim questions on this topic, as I'm sure there's at least one or two that will address all your merchant-related inquiries.
All of the perks that will help you sell stuff easier and to more people are in the Speechcraft skill tree. The ones you'll particularly be interested in are:
Merchant - Sell anything non-stolen to any merchant.
These are all on the left side of the tree, with Haggling and Allure as pre-requisites.
If you want to sell big-ticket items (items over 1000 gold) and you want to be able to sell your stuff without having to worry whether or not you killed Belethor, you need to improve your speechcraft to 100.
There's a quick way to level up Speechcraft:
Once you do that, you should accumulate and spend skill perks on the Speechcraft tree (the 'left' side), and you'll be able to do the following things:
If you're trying to sell at night, most inns will buy food, and some will buy weapons and apparel. The people at the general store will buy anything except stolen stuff, but only in the daytime. If you get a house, you can put stuff in there and go on quests unencombered until you want to sell.