Often it's caused by the bounty hunters fast selling their earned tokens and the price is ruined quite well after this. The best option is to give bounty participants their tokens about 0,5 year later than buyers, it should help.
If all the project would do it then the bounty hunters would have no choice.
The thing is, they will choose a big bounty and those who will pay automatically, for me, I see no problem with that because if there is less
volume the price will dump but it will recover as the project progresses, remember that we are talking of long term projects here.