Here's Something to write about:
Reincarnation exists, focus on an element of the process and spin a yarn about it.
This is more of a
My take on the prompt:

Imagine sleaziest used car salesman you can think of, then magnify it by ten and that is a used Soul salesman. Every religion has tackled the concept of the afterlife but not one has really nailed it. Which means I am going to spill the beans and mind you I could get in A LOT of trouble for spilling said beans, but it's all based of Karma. Yea Earl was right. Over the course of your life you earn karma for everything you do and then when you get to the afterlife you have a choice, either walk through one door into nothing or choose to be reincarnated.

Seems simple right? Just one catch, you do not know what you will be reincarnated as. Even though it is all based on your karma score, you don't know that going in. Add to the fact that your karma score is not one metric but a series of 50 different attributes. Yes, it's very much like a role playing video game. Which makes writer think some of the early game developers beat the system. But that's a tangent for another day.

So once you walk through the reincarnation door, you transported to your Soul Bazaar. This is like a giant Amazon for new souls. Want to be a super star athlete who ALSO is a good person, you better have done something right in the previous life cause it will be pricey. The pricing has in the main stream marketplace has gotten ridiculous lately because of over crowding and lack of production. So most newly deceased are stuck in tough spot of purchasing something cheap like lowly insect or some type of rodent. However if you keep going through the Bazaar you will eventually come to the second hand soul market, the home of used soul salesmen.

The second hand soul market is exactly what it says, second hand souls. You see sometimes souls get returned or a manufacture wants to put out a new model and they have a ton of older inventory so they get sold here. Or the really bad ones will hijack souls on their "path" back to source so they can be 'repurposed'. Sometimes they will get ones in a near death state. Hell they will sale them with another soul still in them! This leads to a weird co-habitation thing and both souls end up back the two doors pretty quickly.

The other thing they don't tell you is that your karma accumulates over each lifetime, so while your memory is wiped, oh right, I forgot about that detail.

Quick side tangent, so when you die and chose reincarnation, your memories are kept in a limbo for the next time through the cycle. Their is a painful series of rooms before you get to the bazaar called transition circles, where all of your past lives memories are joined with your last trip through life. Crazy if you just spent six months living as a beetle, only to find out that in a past life you were actually a in the Beatles. Not saying that's true or that John Lennon might have spent the last 80 years as various insects. Anyway back to the soul cycle...
Haha, soul cycle.

So in theory if you knew the system, you could keep buying the cheapest soul available and building up credit till you wanted to cash in a top of the line model.