What you can do if you like the project and you are not sure of the promises
Save up to buy if you don't have money, you can wait for it when it is listed and dumped, you buy cheap.
Some bounty participants like the project but don't have the money to invest, so instead of investing their money, they will invest their time in participating bounty campaign.
I think some of them aware of what is the risk of joining. And some of them just joining and hoping their time will be paid off.
those participants in the bounty campaign will only provide full support for the project provided, while for investment sometimes there are several bounty participants who invest in the project depending on whether the project has good development or not, because usually only good projects get such supporters.