Looking to buy a house, upon inspection noticed that all 240v use 2 wire plus ground romex instead of 3 wire plus ground romex. Is this proper? All 240v circuits (A/C, Range, Water heater) are connected Black & White as Hot & Copper is Neutral/ground. House was built in 1992. Should this be fixed to 3 wire romex?

New Construction, and Remodel, by code shoud be 4 wire(Range and Dryer)
This separates the ground and neutral, keeps case from carrying current of any 120 volt stuff. When you change receptacle, also get 4 wire Dryer or Range Cord.
Remove strap at appliance connections, Have Green/Ground go to case any whites connect to the white. Red,White and Black will be on Terminals(most likely).

House was built in 1992. I am aware current correct configuration is RED/BLACK each HOT, WHITE Neutral, Green/bare ground. My question was was this correct ever to do Nutral on the ground wire and White as a Hot. Is this something I should get the seller to fix before I buy the house? House is 19 years old and hasn't burned down yet, but It seems to me to be wired wrong in the first place. Im I incorrect?

Only ranges and dryers are allowed by code to use the bare wire as a neutral and equipment ground. And this is only for pre-existing appliances.

These appliances need a neutral for the drum motor, lights and control.

Having a 4 wire feeder to dryer and range is preferred, but not enforceable by code.

AC and water heater do not need a neutral, only the 2 hots and equipment ground, and using the white wire as a hot is allowed. Current code requires that new installations the white wire be re-labeled with colored tape to indicate that is is being used as a hot wire.