I've gotten hit by a RWT ban once, this lasted for 3 days as this was my first offense, so kind of like a warning.
Beside that they took away all my gp that is acquired from that RWT.
If you no longer have the money they could also remove your items worth the transaction.
1: Never trade a low level / garbage account.
2: Never trade on a f2p world, especially not around Lumbridge.
3: I recommend to only trade with "legit" accounts with a decent combat and total level.
4: I feel it is safer to trade with people who are in your clan for a while.
5: Maybe add a few random items to the trade to disguise a trade for absolutely nothing, or purchase the items instead of gp (for example if you buy 500m maybe you can ask for a ancestral robe set, dclaws etc etc)
6: Use a alt account to accept the money on, then launder the money for example through the GE with obscure items. (This will lose some money, but rather save than sorry)
6.2: leave the money on the garbage account, and pay out friends / allies for loot splits off that account to launder the money.
As people mentioned above, there is always a risk of getting banned / chain banned.
The best way is to avoid buying gp, and do the good content to make money! (Selling Nex teaching streams!... hehe)
Good luck and have a nice rest of your day.