Hi Huw, if you are looking at cars that have been well maintained ie belts done, recently motd, with clean interior, nice bodywork, but some blistering or peeling of stonechip on sills, then work may be required, though it can be difficult to tell without stripping the stonechip back to investigate, which no seller will allow. But! if it has a recent mot then it could be said no structural problems. That is not to say work is not required. If you are willing to accept this and everything else checks out then don't dismiss the car as although others say good rust free cars are out there they will eventually need work also and will be more expensive to buy. Remember also if you can see the beginnings of corrosion you are aware, whereas some could be painted over and not visible. I bought my car 3 1/2 years ago without this knowledge, and had small area of peeling and one area where someone had missplaced a jack at rear end of drivers sill. After 3 years I stripped sills back to metal, passenger side had some surface rust with a few peppered areas which were cut out and new metal welded in. Drivers side had corroded round previous filler job and had also affected intermediate panel,cut back to good metal and new metal shaped and welded in. All weld ground down, skimmed, stonechip reapplied, primed and painted. Then applied Dynax to sill cavity to protect. Cost £350 for paint, £140 for labour(welder freind) £50 for metal sheet, grinder blades etc. £30 for dynax. PS. Sills from Porsche are £156 each. Hope this helps, Alan.