He's bullshitting you in saying that he cannot fit non runflats to cars designed for runflats,but, that may be what he's been told.Any one can fit non runflats, its your choice as a consumer as to what you fit.It may not be recommended, but that's only because they are harder to fit on runflat rims. Runflats have only been adopted by car manufacturers because rims are getting so wide that spare rims are impractical and they didn't want to go the spacesaver route.No spacesaver saves the manufacturer cash and weight in the car,so they can package the car differently.It's not really a safety issue IMO,just the packaging of the cars.Fit whatever you want, it's what most of us on this forum have done/are doing.