I believe major platforms have ways of manipulating the market,  but they all have their  limits. I doubt  how a reputable  platform  like PayPal  would try and do something  of that nature.  Nevertheless,  should they involve  in a falsification  of the real amount of bitcoin,  they would easily  be  exposed.  So far  as, no one has complained  of having experienced  undue delays in withdrawal of bitcoin,  then everything  is fine on the platform.