A couple of questions:

Where was the car driven? There is a world of difference between driving in Mexico City (D.F) and elsewhere in the country. Each situation poses different issues.

Does the car have maintenance records and is maintenance up to date?

What firm did the armor work, and can you get a receipt for the work done? There are firms that beef up car suspenstion to handle the extra weight, but I wouldn't count on it unless you know it was specifically done.

In general, my experience with a non-armored car in Mexico is that you should estimate the mileage as double what you read (or more) to take in to account the driving conditions in Mexico.

Regards
John

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles