If the buyer decides to sell the previously purchased steaks, then who will have the obligation to put coins?
The logic: by purchasing bounty stakes, the buyers take the same rights (and risks) as if they were bounty hunters. Simply saying stakes buyers pay for not doing bounty work but take the same rights & risks as all other hunters.
Not agree about risk. Bayer loses the real money, hunter loses a time. It is not the same risks.
Only a user who had initially deposited 'collateralized' stakes has an obligation to put altcoins of a related bounty project.
Note that this user may also buy back stakes of the same project at any time in order to settle his initial obligation. It will help him to avoid loss of collateral in case of inability to put altcoins in time (for example if a hunter was banned or got red trust or whatever).
Regarding the risks you're right, but stakes buyer covers his risks by buying stakes for a hughly discounted price. This is an ideal evaluation of any project that appears in the market. So, besides the main purpose of Bounty stakes Trading, the stakes prices fluctuations will be the best ICO/STO tracking tool ever existed. It will show how the market evaluates a project at any point of time.