Having rented in third world countries many times, it is imperative to take a video or photo of the entire car, including close-ups of tires, bumpers, etc. I do that every time I rent a car, no matter what. Strangely, the idea first came from Sixt when I picked up a car in MEX. The lady there suggested I do it so it's kind of stuck with me since then.
I have never encountered such a problem with Sixt despite renting from them numerous times in LHR, FRA, and now TIJ and MEX.