I bought a bike from Halfords for my grandson but couldn't have it for
two hours as it had to be assembled by properly trained mechanics. I
got the bike three and a half hours later. On getting home I found
that the front wheel was not properly attached to the forks, and spent
the next couple of days taking it apart and reassembling it without the
instructions as Halfords had kindly removed these for safety purposes.

I'd insist on the instructions!

I'd also very carefully check a bike first