Bounty restrictions can fix few problems facing project price drop after listed on exchange,
1) if any dev want to avoid dumpers then they must limit bounty participants, the limit the participants they better ,if a bounty only request 300 participants at highest and the 300 became a dumper it won't hurt ,unlike 2000+ participants
2) devs should forget bounty when still on ICO ,allow bounties after your project finished ICO successfully and make your project is doing great before allowing bounty
This are just ideas ,if you have anything better please drop on here and let's share.
I support your both the points but bounty hunters are not the dumper for your kind information, check projects like HYPERQUANT (
https://coinmarketcap.com/currencies/hyperquant/) & there were so many projects which distributed bounty rewards after 1 to 3 months listing on the exchange & their values were almost 80% down. Bounty Hunters are always deceived by the projects as they get late rewards & blame for dumping which have been proven with the recent projects that investors too dump the coins/tokens on exchange. Also the total allocation for bounty campaign ranges between 0.5% to 5% which I feel doesn't affect the project.