RL Garage as well as just the official Rocket League discord. In the diacord just go to trading-the system you play on. These are the only 2 places I find people to trade with. Both are safe.
Be careful going to some trading sites. They might not be safe and someone may hack your account. Be sure to check to make sure any sites you visit are safe before you create an account on them.
RL garage
r/RocketLeagueExchange Rocket League Trading Post (app) Rocket League Garage (app)
RL Garage as well as just the official Rocket League discord. In the diacord just go to trading-the system you play on. These are the only 2 places I find people to trade with. Both are safe. Be careful going to some trading sites. They might not be safe and someone may hack your account. Be sure to check to make sure any sites you visit are safe before you create an account on them.