To ensure you don't get scammed use approved marketplaces like BHW. The main thing to worry about is to ensure that the user is reliable and known and that the channels they are selling are in good standing and not hacked.
Main thing to check on the account is to check if the channel has any strikes or that the content uploaded has been copyright claimed etc. Just ask them to screenshot their monetization page.
Also you need to remember when you are purchasing an account from someone, transfer the ownership to a new e-mail. If its a personal account get them to change it to a brand account and buy an aged PVA account from BHW and move it to that account.
The main reason you do this is to ensure when the person sells you the channel it will be tied to their phone number usually. If you don't change ownership it will still SMS the old sellers number to complete the actions required with phone verification.
To get rid of this issue the owner of the channel needs to transfer ownership to another e-mail to your google e-mail ID from his computer and you need to accept it making you the new owner. Then you will need to stay the owner for at least 7 days in order for the transfer to be successful for your e-mail to become the new primary owner and to remove the previous primary e-mail account.
But obviously pay him the money first and get his channel and email and log into it. Do the ownership transfer steps by yourself.
If you want to ensure you are not being scammed you may want to organise a payment method with the owner to release the funds after the 7 days, but ensure you do notdelete any of the old channel videos as they will help with ranking authority in youtubes algorithm.
