It would be best to Do more research before participating on any bounty, ask questions to make sure that your effort won`t be a waste in the end.
All rules are written on the first page so just read it first before joining and continuing with the bounty you have chosen to ride. And if at the end of the bounty you never receive the tokens, have you ever ask when the distribution is?
Sometimes there are bounties that are requiring KYC and they will never send you tokens if you never confirmed your account to them. That's their way to eliminate cheaters but for some airdrops, it is not worth it.
As a participant you should really be keen on receiving updates which are usually can be found on their telegroup or any mediums which they do actively give updates.
If you have failed to followed those groups then you would most likely to missed out the updates which would lead into failing of receiving your tokens.