I am pretty sure that both accounts would be banned since both would be accounts from one individual. The staff can easily see if that is the case.
I do believe you should be given enough ¥ to match market price but not given the actual Pokemons back if they were sold. The one who bought them did so fairly and might have sold them too which make the whole process more complicated.
In any case, you always bear some responsibility once you decide to use one of those services and the lost ¥ will probably act as a reminder for you to be more careful. You can always find mostly trustworthy trainers with many reviews on the forums, I believe you would be more safe with them than with random people advertising in chat. But once again, nothing is 100% safe in trading for services.