What to consider when staking another player?

Edit. to my response to AidaBosa.

In here I made an error. Naturally we have to deduct 50% of the buy-in from horse’s profit. So in scenario a) the profit is also $5.

What if a player sells more than 100% of the buy-in?

That’s obviously not a sustainable scam, but that doesn’t mean people won’t try it.

yeah, thanks for explanation)