As you know, there are three factions which are Aldmeri Dominion, Daggerfall Covenant and Ebonheart Pact in the game. In general, you are not able to do business with others when you are in different factions in almost all games. But in this game you can trade ESO Gold and items with anybody at any faction with the following way.
If you are in Aldmeri Dominion and want to buy an item which belongs to a seller in another faction, you need to find the Bank of Daggerfall first (You can find a bank in any cities) and go there to talk to NPC. Select the Bank option then deposit your money you want. You can put the items which you want to trade in the bank too. Then log out the game to choose the character in that faction which is the seller in, (If you haven't got a character yet, then create a new character in that faction. Now you need to do some quests then you can get out of the born place to the city.) then find the bank and talk to the NPC, you can find that its possible to withdraw the money and items which you have deposited by your main character. Withdraw the gold or items that you want to trade
After that you could contact each other to trade and accomplish it well.