I usually use the hut in Scyda Neen that you kill a guy for tax evasion. He is not home being dead and his containers in his house do not reset afaik. There is probably other places like this non-resetting.
One trick for expensive items is to go to a trainer that buys items. Then you pay for training so that their gold skyrockets and then you sell the daedric items out of their huge money pool.
Another trick which I think I forgot some details...
When you have money buy emeralds or rubies and then I forget how the alchemists reset their stock, but there is a way to give back the gem and you can get that merchants stock in rubies to go up to 99. You can't sell the daedric weapon to the alchemist, but you can convert money into emeralds. Then use the emeralds as 'change' when you sell a daedric weapon. So say you sell off 50 rubies and are bursting with money. I'm not sure if there was a way to make change with the rubies for the daedric weapons, but you can certainly 'make change' for when you make tons of potions for sale to the alchemists. My characters are usually walking around with tons of rubies in the pocket.
OH^up^ now I know how to make change. Buy an enchanters entire stock of expensive items which makes them have high gold. Then sell the full value daedric weapon. Next travel to other enchanters and sell them the junk items you don't want. It takes some effort, but there are a lot of enchanters and you can make oodles of money which you can use to train and soon take a higher curve towards power.
Finally there is creeper in some city in an orc community dwelling. You can search 'creeper' in the wiki. I think he has a lot of gold and he pays out the money for the face value of the item, without the imbalance of goods you sell at lower price than buy.
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