Someone told me that I can be banned for trading keys, is it true?

We have 90k users on SG and we have members with high valued accounts that make uses of this practice, so we'll never face any problem because of this!

afaik most devs/pubs don't care about trading as long as its non-profitable, i.e. selling. even a small trade-up wouldn't bother most. but if you trade for paypal/money, then you're treading into their territory and would have an issue.

for personal use in general doesn't literally mean only for said person to use. it means not for commercial use and non-profitable.

Trading items outside of a secure Steam trading window, such as keys, is not in itself a bannable offense to Steam. They have "washed their hands" of such trades, denying liability even if keys in such trades are revoked. This, in a twisted way, protects scammers as Steam offers no support or assistance, as they have warned users time and again that such trades cannot be policed. However, they do have a history of exceptions in cases of habitual scammers that they can track (chat logs are stored server-side, transactions/chargebacks leave records, screen names may change but ID cannot be changed, etc.).

As long as you are an honest trader and your keys are good, you do not have to fear being banned for trading keys. Someone could try to troll you and report you to Steam for trading keys and nothing would happen to you.