If you think this is a scam, you are clearly mistaken. I can explain mathematically.
Firstly, lets assume when the time comes, the soul is important for whatever reason. I will no longer have one. You can do whatever you want with it. The person who judges my soul clearly knows it was sold.
Whether you believe in a soul or not is irrelevant since we can not know. So if a soul is real, there is high value to it. The chance of it being real and having value is non-zero (it can be big or small, but can't be zero). So there is a balance between odds and reward. In this case, the reward is near infinite, and the cost is what the bidder deems appropriate.
I hope this makes sense.