If the tire repairer can not determine how far and fast you drove with it flat, then he can't be sure whether there was damage to the tire from heat, and it is safer to replace it. He isn't necessarily trying to make more cash, just doing the prudent thing.

Run flat tires are designed to get you safely to the side of the road, or the nearest repair facility, not to continue driving on.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue