Concur with the advice above, and I think all you can do is approach breeders and quiz them very thoroughly and be very very skeptical. Be prepared to walk away if your gut tells you even if cute puppyness is pulling on your heart strings!
Good signs:
-The breeder grills you more than you grill them, with our breeder it felt very much as though we were being interviewed to see if we were worthy of getting one of her pups rather than vice versa!
-The breeder has pretty rigid conditions/contract for letting you take a pup e.g. pup not to be bred from, if you ever can't keep pup they will take it back even as an adult, how many visits you must make before taking pup. Our breeder was arguably a bit OTT in that she doesn't let people choose their own pup from the litter, she 'matches' you with what she thinks would be the best personality/type, some people wouldn't like this (my DH didn't!) but it's all part of her true care/love for the dogs and desire to ensure it works out for all concerned.
-They have long waiting lists and don't breed more than 2 litters per year, all pups usually spoken for pre-conception so you may need to wait 1 year +.
-Breeder plans to keep at least one pup themselves from each litter.
-Breeder familiar not only with potential pup's parents but also grandparents and wider family, can speak convincingly about their reasons for choosing that particular mating (whether that's for show purposes, work/sport or simply to produce nice family pets). They speak honestly/openly about any potential flaws in either parent (whether health, confirmation or temperament) and things they are trying to improve on or see in the pups.
-Breeder can produce/share full details of health testing of both parents and speak openly/honestly about any health issues in the breed - we have a breed that has some well known issues and our breeder is super passionate/angry about trying to eliminate these and the inadequate efforts of some of her peers in doing so!
Bad signs:
-Breeder has puppies immediately or imminently available, including tall tales around 'oh the last puppy from this litter was sold but the family had a change of circumstances so I have just one available but will go quick, make your mind up today' or any other hard sell/pushy sales tactics
-Breeder doesn't ask you much or seem to care too much about suitability of your home, e.g. if you have young children they just say 'oh that's nice, a playmate' or similar, rather than asking how you plan to keep everyone safe, make time for puppy training etc.
-No health tests of mum/dad or vague 'my vet's checked the puppy and says it's healthy' type scenarios. Excuses given or no/vague details provided re pedigree papers/registration of pup and general heritage of mum and dad.
-Breeder appears more concerned about ensuring they get their cash than other contractual issues e.g. re return of pup if anything goes wrong, or no contract/paperwork provided at all.
-Mating appears to have been chosen on basis of what will sell e.g. a fashionable cross or to ensure pups are 'cute' or right colour OR from convenience, e.g. they already own the dad or their mate does, rather than health/suitability of pups.
-Breeder appears to openly advertise on facebook/gumtree/preloved or other selling sites, IMO good breeders may post about their dogs on breed pages on social media etc but have little to no need to actively 'sell' their litters as people come to them, demand outstrips supply...
-Needless to say, all the classic puppy farm signs e.g. puppy can't be seen with mum or 'stunt mother' is used, puppy appears dirty, sick or to have been kept outside or away from family environment, very young puppies for sale, breeder sells more than one breed without good explanation etc
Good luck!