The seller offers to me holding the funds up to 1 month after the account logins were given to the buyer. This is to increase trust in this offer.
If someone can help with how easy it is to move, or sell, software from one account to another account then let me know. I remember that some years ago a friend of mine bought a used steam game on ebay. It was pushed from the owners account to his account and it was without problems. I remember that at that time everyone claimed that this is not possible but in fact it was possible, only steam didn't like that possibility very much and did not promote it.
Does anyone has experience in this?
Not too sure about a few years ago, I wasn't as active on Steam 3-4 years ago because I didn't play TF2 and steam wasn't as big back then prior to DOTA2 and CSGO.
As of right now, I don't think it's possible to "push" or transfer games that is already in a steam account's game library. Steam games can however be "gifted" to other steam users, but this means the game is in the inventory and not yet "activated" on the account.
So basically the games on the account right now cannot be transferred and will stay on the account forever. And I do believe it is ultimately against Valve's terms to sell/trade steam accounts, they can ban you if they find out.
I don't think there's a 100% safe way to purchase steam accounts. Buyer will always be at a slight risk unfortunately, but anyone who buys steam accounts should be fully aware of this. I have purchased steam accounts in the past without any issues, but that is because I look for reputable sellers to help minimize the risk of having the accounts taken back by the original owner.
Oh, one thing I forgot is, if the original owner of the account can provide the e-mail account associated with the steam account (the one that was used to register the account initially) then it can help the new owner in securing the account for himself if anything does arise in the future.