Given the fact that there are several diseases of intrest to watch out for
I would select a seed stock (registered) producer who sells cattle that are older or are not quite quality to sell as registered as commercial females, have them bred or bred with calves at side, also get evaluations from a vet
get length of pregnancy confirmed, vaccination history, get blood tests for Johne's, Bovine Leucosis, Bangs, TB, herd health history on animals you are interested in, ie age at first calving , production records, with est. birth weight of each calf, if they can't provide this stuff, find someone else to deal with or you will end up with someone elses wreck,
and also ask if they can recommend some competitors to looks at as well so that you can see what other people raise, and if they are better you will be back, that is what I do any way, and if the other guy has better, then you did your self a favor, if they won't offer up at least one or two competitors, they are affraid of losing the sale, probably because they have mediocre cattle and know they will lose the sale