Don't try to purchase directly from the artist represented by a gallery. That puts the gallery and the artist in a difficult spot.
You could jeopardize their professional relationships and your standing with dealers, which could affect your ability to purchase works in.
Do: Request a condition report
Whether you are purchasing from an auction house, or directly from an artist, it's common to request a condition report for the artwork you're considering,
For historical works, especially from the "secondary" market.
There is no norm for condition reports. However, there are some guidelines. Many condition reports will include diagrams, for instance.
The artwork must be noted for any scratches, marks or tears. Here's an example condition report from Georgia O'Keeffe.
It might be worth it to hire an independent third party to conduct the report on condition based on the value of the item. However, this would increase the price.
You will probably have to pay to use the service.
Art collectors who have an Artwork Archive Premium Collector plan can digitally store condition reports for their pieces by using "additional documents"