Check all electric window switches to see if they work and door locks too.
Look carefully at headlights and taillights for evidence of water.
And mud means flood, look everywhere for it, they'll scrub the obvious places but can't get it all.
In 1981 I left the Air Force for two years to finish college so my then-fiance needed a car. Instead of waiting for me to visit her during Spring break she went home to Texas and her overbearing jerk of a father bullied her to get a car there and he pushed her into a used 1970s Datsun 210. The car was messed up and had aftermarket pinstripes.
When she got stationed near me I went ahead and opened up a rear inside panel to run some speaker wires and found about six inches of dried mud and a dealership stick-on from Florida. I then found the pinstripes covered where the sheet metal had been creased and the car repainted (badly).
The POS car had been a hurricane car from Florida. No Car Fax back then, heck, no computers either.