unfortunately testwise theres no actual requirement to advise anything and even less incentive to do so when selling it as you’ve found out.if however there are defects that shouldn’t have passed that’s a different story.contact the dealer in the first instance with your concerns.if you get no joy then dependant on time since test an appeal via the ministry is a possibility as is trading standards altho there are many restrictions on time/condition etc regarding what they can and cant do.as regards getting your money back that’s gonna depend if the dealer misrepresented it.if(for instance)you’ve bought a 15 year old transit with 150 thousand miles on it then its gotta be expected to be near its end.a 4 year old astra with 20k on the clock would obviously be expected to be better.its a 2nd hand vehicle not a new one and that would be a factor in any of the above.the guy who sold it(and took the money)has to be your first stop.