So, I bought some games as a gift and I got a certificate number to claim them. The problem is, if I want to trade each individual game with different traders how do I send one game to each one of them?

I mean, the number is for a gift that includes all games. I know you can claim each one of them individually checking a small box, but if that is the only solution, that means that from now on if I want to trade these games individually it will be a trust based deal. How would you prevent being wronged in this scenario?

Any advice?

I think you can ask support to split the code - there is no other way.

Would you trust the person you are dealing with if it had good rep?

I'd never fully trust people from the internet. ;)
Good rep is ofc "ok", but there are random chances that, for example, someone hacked his/her account.

Yes, possible but unlikely... Either way, many thanks for the advice!

Thank you for the link!

Add this to your bookmarks as well!

Check the google for user name in question.
When you search - do not type the name - instead COPYPASTE it in search engine. Many scammers try to impost legit users by adding similar looking or extra characters.
Do not start trading in chat, start trading in trade thread. If you are contacted via chat, require the user to post in trade thread or link to his posts there!
If user is recently registered or has no _proven_ _forum_ trade activity - he sends you the keys first.
If you are both recently registered you might want to exchange a key for a key. Still, if you send a key first you risk to loose this key. So you might want to limit your trade only to those members who have established good reputation as traders (do not confuse with forum reputation under user name). Do not go "all-at once" under any condition, unless the user is valid AND very well known to be trusted.
Do not trade with anyone recently registered, since you yourself have registered less than a year ago.
Maintain own list of successful trades and check others for such list.
Check his forum presence, check his trades, check his mental ability. No forum posts or vague forum posts - no trade.

Good members value their goodwill and forum reputation much more than all the games. Games/codes mean little to them.
Scammers value the games much more than goodwill or forum reputation - codes are the only thing they care for.

Very usefull tips. But now I have additional questions.

How do I check rep as traders?

How do I create such "successful trade list" or check one from users?

Thank you kindly!

I have linked you to the thread with successful trades lists. Also, the traders often list successful trades in the trade thread. Each of the entries should be verifiable from both sides:
1) A thanks B for trade,
2) B thanks A for very same trade ,
3) and both of them are very known.
1+2+3 = valid.

You can limit google engine by appending "site:xxx.xxx" to inquiry.
For example:
[url=https://www.google.com/#q=lin545+site:gog.com]https://www.google.com/#q=lin545+site:gog.com[/url]

You can also search the individual thread for user name, using "search" function in the forum.
https://www.gog.com/forum/general/gogs_general_trading_thread?search=lin545

As always - do not type the username manually - use copy-paste.

Again, thank you very much for this. Didn't know about that google engine search tip!

You are welcome! Have a great time!