While I can totally understand your frustration a thread like this isn't doing anyone any favours.
Did you ask him what accuracy & grouping he had got from it with what pellet, & try that yourself ? perhaps a mod could now do so on your behalf
I would hope the seller did not sell it knowing it would not group when he could just have taken it back for any fault to be investigated.
I actually had a very similar situation with my FAC Rapid .25, I think it was only sold because it was so inaccurate & had I tried it first, I probably wouldn't have bought it,
But
once I got some JSB kings it's pinpoint
it just won't shoot any other pellet, quite possible this rifle is equally fussy.
First thing is it needs to go across a chrono to see if the muzzle velocity is steady, then if it is, have a serious pellet testing session.
Perhaps another member close by might give some help & a fresh opinion.