Wily, a few things to consider.
While it happens in all auctions, it's seems more prevalent in the dogs that there will be plenty of 'buy backs' .... breeders just put their dogs through the ring to qualify for the race series.
Breeding is one factor but unlike horses it's not as critical in dogs, yes a good line is a chance of throwing on but more important IMHO is the dams ability to run.
There was stats produced 10 or so years ago that stated you were something like 1 in 35 of getting a city winner but if the dam of that pup is a city winner herself, the probability comes down to around 1 in 9.
I used to have a time standard of 30.60 at Wenty, I wouldn't breed or buy from something that couldn't run that. That time has obviously changed with the track improvements, so I'd say that a minimum would be 30.20 or even closer to 30.00
So look for something that could run, more than something that was related to this or that.