Agree with G&L, as you go the the sale, go early and look closely at the cattle, remember that although most cattle sold there are sold as healthy feeders, etc, there are plenty of culls being brought in to sell as well.
If you can see them being unloaded, you can often ask the seller about them.
If not, look at the body's and score each one in your mind, look for any tell tale signs on respiratory problems, that is heavy or rapid shallow breathing, runny noses, noses that contain green or yellow snot, or excessive mucus, Also look for chapped or red noses, running, or watery eyes. Are they standing normal and erect? or stretched out and oddly standing? Hunched up?
\Look at the hair coat, is it in good condition> is it in a condition to match the current season, ie: winter coat for winter time, summer coat for warmer weather. When cattle do not get good nutrition, often the hair will show it, being dull, patchy, and or, delayed in conversion to match season changes. Any obvious signs of external parasites?Bald spots? shedding areas?
check out the tail head, fat? good condition, or sunken in?
check the manure either as it poops or the stuff that is still on it's butt and tail, look normal or excessively fluid> blood? other odd coloring?
( often cattle being shipped will get runny manure due to stress)
check the reproductive organs...normal? or enlarged? puss? injuries?
see it walk. alot of cattle grow wheels after they have injuries to the pelvis, legs and or feet. look at the feet, hooves ok? or growing oddly?
Just as you would check out a car you want to buy, give any cattle the same attention. Mechanics can fix your vehicle alot easier sometimes then you can repair or make healthy a broke down or sick cow. Been there done that.
Good luck in your purchases, and don't let anyone push a looser on you.