@ACavalierDream thank you, I'm really glad you found it helpful!
I would only add one thing:
- The first dog of a breed, or puppy, that comes along and you see may well be the best - but it may well not be. And it's okay to walk away. People always say 'but the puppy/dog was lovely' (even if the 'breeder' was a walking red flag) and they want to help...but by buying that puppy or dog and taking it away from an awful situation, they are enabling the 'breeder' to continue abusing dogs. It's better not to buy or rescue a puppy or dog if you have any concerns than potentially ending up supporting a nefarious breeder or buying a dog/puppy that is not healthy and finding yourself landed with hugely costly vets bills.
On the 'advertises online' this is a bit nuanced and some excellent breeders do - but they absolutely won't have entire litters up that are all available. And they will never, ever, use Pets4Home, or GumTree etc. They will use ChampDogs or the KC Website. They might advertise in advance of the litter being born, or one or two puppies, but almost certainly not all. And anyone with more than one litter or one dog up at a time will always be a puppy farmer. Raising a puppy or dog right takes time and patience - if there is a high-turnover of dogs or puppies, it means the animals are not being looked after properly. Any breeder selling an adult dog should be avoided, IMO. Mostly it's just common sense but it's so easy to get sucked in!
Ultimately, finding an adult dog (if you are determined you want to rescue, @Eeehbahgum ) is hard. Going through breed-specific rescues is your best chance of knowing exactly what you are getting. People who sell privately (i.e. Pets4Homes, Gumtree) or big charities are often less than honest about the dogs behavioural issues and experiences and health than the breed specific rescues. Sometimes that's deliberate and sometimes they're just incompetent.
The breed-specific rescues will have had their dogs in foster care, where they will be carefully examined in a variety of situations (other dogs in their home, children, cats, small animals, recall, walking to heel) and also checked for behaviours (guarding, aggression, nervousness, shadow chasing) and therefore they will know exactly what the dog is like.
I think it's really important to take dog-buying seriously in general...but if you're going for a dog/breed that is known to have lots of health issues or be disposed to behavioural issues then it's even more important. Bichon Frise are prone to a varitey of expensive, life-limiting health issues including luxating petellar, hip dysplasia, glaucoma. In a worst case scenario if you buy an unhealthy Bichon you could be looking at £20K worth of surgery easily.