on the issue of Gays, that you earn 10% of the value of an item sold, I have a doubt: If a player buys this same item, only within the map through the "MarkerplaceService: PromptPurchase" , will I also earn that same 10% of that sale?
No. You don't get 10% because according to the Roblox forums Roblox released a new marketers that you can get. If you have premium layouts you will get 10% or purchased apps. But if you don't Roblox will take 70% of your robux meaning that you will only get 30%.
I'm not entirely sure but I do know it depends if you made the model or not taking JesseSongs comment I'm thinking that yes but I wanted to add it could be a possibility of you not owning the item so like back in 2017 it would ask if you wanted to sell gear with your game it told you it would give the robux to the owner
The following is true if you have the tool/model in game and is not true if you are getting the tool/model using a id.
Yes, you will get a profit because roblox thinks that you have created that tool/model and you will get more than 10%.