most people think they deserve higher elos, but are kept down with teammates etc
sometimes it's true, but i'd say in 95% cases it's not the case.
my mate was silver for 3 years, bought a boost to plat and climbed himself to d4 afterwards where he proudly gatekeeps now.
sometimes people are good, but don't have a 1v9 potential in them.
in most cases , they'll mess up their mmr after boost and end up in their real elo next season^^
https://euw.op.gg/summoner/userName=Velveckhere's a case of player buying boost in s9, then playing by himself s10