i think some replies you've gotten pointed you to head to a panel beater approved by the car manufacturing company.

the idea behind that is so that they have the ability/knowledge to restore the chassis to within manufacturer's dimensional tolerences.

there has to be a compromise here. one cannot expect the same physical properties of the metal to be maintained once the deformed metal has been worked in (ie. repaired). quality of the metal is obviously sacrificed but if parts of the metal being repaired have not sheared off which will result in welding the area, the repair could be acceptable.

depending on the quality of the repairs, you may experience stress cracks developing around the areas where repairs were made to the structural members of the car. the most common would be degradation in the welds made during the repair (ie. surface not prepared properly prior to welding or porosity of the welds just to name a couple).

if at all possible and costs aren't too high, you ought to consider engaging a third party inspection company to survey the damages.