Good luck getting any of that sorted to a "high standard" and anything other than a cheap ditchfinder tyre fitted. They'll do it as cheaply as possible.
As others have said, you made the mistake of putting down a deposit before attempting to negotiate, when it should have been the other way round, therefore I highly doubt they'll entertain lowering the price.
As others have said, you made the mistake of putting down a deposit before attempting to negotiate, when it should have been the other way round, therefore I highly doubt they'll entertain lowering the price.