I think the "blanket" answer is be upfront, ethical, and honest in anything you sell. Don't misrepresent what you are selling by knowingly hiding something or marketing it as something that it is not. And with virgin heifers and bulls, a good seedstock producer should guarantee 1st year of breeding, if a heifer won't breed in normal conditions or a bull is firing blanks and can't settle cows then they should refund or provide a comparable replacement. That's just my feeling at least, when you are in the seedstock business your reputation is everything and not making good on a deal that went south for 1 reason or another could hurt your reputation more than what the animal is worth.
I think Butch and Raven are dead on with what they said above, buyer needs to at least have some obligation of his own to do the homework on what he potentially is buying and as Raven said quality is in the eye of the beholder. For instance when it comes to udders, what 1 guy may find functional another may not. Obviously when it comes to heifers or dry cows it's harder to judge udders without knowing a little about the breeding behind them. As for feet and structure, well what you see is what you get - it's hard to hide what is staring you right in the face if you know what to look for. When it comes to a seller you'd hope most would be ethical and know what is worth offering up and what should be culled and sent to the sale barn but that's 1 thing that unfortunately is mostly something that falls on the shoulders of the seller to do the right thing and can't really be "regulated." If you have questions a seller won't or can't answer like weights or any data they may have collected, general questions about how they raise their animals, etc. that should be a red flag.
Like callmefence said about 700lb weanlings, I'd want to know was that obtained by using creep or not and how long were they on creep before weaning. How about their mommas, what kind of management system are they raising their calves - what kind of body condition score and how much added nutrition are the cows getting and what kind of environment are they raising their calves in? So many variables can potentially "prop up" weaning weights that these are questions any knowledgeable buyer should be asking and taking a visit of the operation to see for themselves so they have a good understanding of how what you may buy was raised. Any reputable and honest seedstock seller shouldn't have an issue with showing you their program and answering any questions you have.