Establish the factory starting point
Before deciding whether a car is modified, you need to know how it began. A build sheet gives you the recorded paint, trim, wheels, equipment and option packages for the individual vehicle—far more reliable than judging from what “usually came on that model”.
Walk around the car with the report and note the differences. Prioritise expensive, mechanical and safety-related areas before getting distracted by phone holders, stickers and other harmless evidence that a human being has owned it.
Look closely at the visible changes
Common modifications include wheels, suspension height, exhaust components, lighting, bodywork, seats, steering wheels and infotainment. Check the quality of fit, tyre sizes, warning lights and whether the seller still has the original parts.
Factory-looking does not always mean factory-fitted. Many excellent retrofits use genuine manufacturer components, which is precisely why a visual inspection alone may not settle the question.
Software leaves fewer fingerprints
Engine remaps, gearbox software, feature coding and emissions-system changes may not appear in the option list or reveal themselves on a gentle test drive. Ask for invoices and use appropriate diagnostics where the risk justifies it.
Relevant modifications should be disclosed to the insurer. Undeclared changes can affect cover, warranty and resale, even when the work itself is technically impressive.
Modified does not automatically mean bad
A carefully chosen, well-documented upgrade may improve the car for an enthusiast owner. Poorly installed or unexplained work adds uncertainty. Judge the quality, legality, reversibility and effect on maintenance rather than condemning every non-standard bolt.
The factory specification establishes what changed. A specialist inspection establishes whether it changed well. You need both answers before deciding whether the car is an exciting find or someone else’s unfinished experiment.