The genetic guarantees I have received show pics of both parents, along with a picture of the animal I have. It also includes both the DOB and the clutch number from the breeder. The wording goes something like "This serves as a genetic guarantee that the animal in the image below is a [sex] [morph] ball python, captive bred at [breeder]." Last, but not least, the guarantee is signed by the breeder. This particular breeder also has clutch pictures available online, so that helps back up the guarantee.

When buying/selling hets, you can't possibly have too much information or have too good of a reputation.