Advertising on this forum should use an escrow established and also known on this forum, that would be the best practice. Medusa is a really high value item, I think a long known crypto escrow from Bitcointalk would consider handling the deal if asked. Steam in my experience is wide open highly trafficked by the whole spectrum of users from normal players to professional gangs who make it their work relying on users not deploying best practice.
Its a minefield, I advice extreme caution; Im glad to see anything Csgo related and Im not commentating anything specifically
Will always accept use of escrow