My findings on this are that Mysus, the Merchant in the Black Market area (Also the Lockpicking trainer) In the expansion FLAMES OF VENGEANCE Content.
He Resets his inventory on a Cell Change meaning if you leave the area and Quick save / load and Re-enter his domain you will be given a new selection of items to purchase.
A Great Way to do this quickly is using your dragon stone to go to the battle tower and then returning after a save and load. (The reload resets the temporary data)
As is the case with all items in the game, they are generated by coming into contact meaning that his items are different if you quick save right before speaking to him. (This helps the farm a lot)
The way his item statistics scale is based off of level as are with the bracket system of the original game. The level cap is 50 for Bracelets, Necklaces and Earrings. The level cap for Rings and Belt is level 52.
IF YOU GO BEYOND THIS THE ITEMS WILL NOT HAVE STATS.
The stats are as follows. .13 regen 7 crit 85 Hitpoints or mana for the Rings and Belt. 12 Dexterity - Ranged Damage / Intelligence - Magical Damage / Strength - Melee Damage (These will always be paired) And +3 Skill points (Random)
After hours of farming I can assure you the skill points are influenced by YOUR selected Skills. Choose wisely, however you can always retrain (only up to a certain number of times due to gold cap)
Finally, your gear stats also have an influence on what stats roll.
I do this in pain revealing my secrets because I wish to pay back this post years later for helping me.
Good luck farming!