I sold my lvl 650 tyranitar a couple of days ago but i checkes the buy pokemin page and my poke isnt there... i also didnt recieve any cash

if no one buy them within a certain time frame, the pokemons will be deleted from the game and you dont get any money.

It was only there for a very short time... like one day

I think the time frame is a day or two. Honestly no one really buys pokemon that high because is over the max amount of money and the prices doesn't goes down, the Highest level you can put on the buy page that under the max money is little less then 600

Edit:I have ShinySnorlax at level 605, and the price for it if I sold it would have been over Max money:

ShinySnorlax M 605 $2,224,725,600

Max Money is $2,147,483,647

so even if your pokemon didn't get deleted from the buy page, no one would be able to buy because it was over the max amount of money anyone can buy.

Ugh what a waste lol... well thank u