Is trading in-game items with other players using Robux against terms of service?

A question i have is that is it against ToS to pay an another player robux to get an item ingame?

Something like this:
Person A and B are playing a game where you have items and there is no ‘trading system’, only just dropping items or giving items to people, what happens if A pays B X amount of Robux so that they can give A the a rare item?

Should A and B be banned?

Yes, that’s essentially a black market deal that most popular games with trading have and also applies to selling in-game items for real-world currency. It would be okay if they used in-game currency to purchase the item. Take Pet Simulator X for example, there is a website independent of the company for the values of their pets in the form of in-game currency (gems) which is totally fine.

They could be banned from Roblox, but honestly Roblox won’t go after people for that unless it becomes a problem with everyone doing it. There are tons of instances where people pay their friends for an in-game item, and while not technically allowed, it doesn’t hurt anyone and Roblox isn’t going to care. Don’t mention anything about it in your game or Roblox will ban you for encouraging it