You can Deffinetely "sell your soul" but it's not what you think it is. Your "soul" is essentially yourself. So by selling your self to an entity, you become literally their property and you are bound to them; which means they control you. Some people say if you do that the entity can devour you (destroy your "soul"-destroy you). I don't know if this is true or a myth though.
It's not worthy of doing it, trust me. I don't know why you want it but avoid it, it's stupid. And yes, if the entity which you are bound to (because you "selled yourself") gives you the permission that you are intependent again then you stop being under the commands of this entity. Which means "you are not selled anymore".
I just don't use these metaphorical terms because chances of someone judging wrongly and considering something not existable are increased. The word "soul" lately too started pissing me off for no reason.
You cannot sell your soul. Anyone who says otherwise is lying to you. They will tell you to message them, only to feed you lies. Nothing will happen, you will gain nothing. In fact, wasted time is all that will come of it.
In hoodoo there is person called the "Devil", but in actuality he is offshoot of an old African spirit of the crossroads. According how he works is that you come to the crossroads nine nights and wait for him to come. You bring something you want to get better at like a guitar for music or dice for gambling. If he appears you give him what you brought and he " fixes" it. Do you sell your soul? No. You just have to pay him for his time, but I forgot how that worked. But this is just a legend.