If I can recall correctly there is an issue with selly. I mean auto-buy service always wouldn't be a good idea where the funds directly go to the seller. If you take a deep look on the scam accusation board you will find many threads that people are scamming from selly. Although selly itself isn't a scammer it's just full of scammer due to no escrow service. I am not familiar with any service that you mentioned. Do you have any deep research about them? Or just simply posting from the Google search list? If you have experience with these auto-buy sites then please add more details. So we can prevent a few scams.