Hey 
Can we please not assume that all dogs rehomed via free adverts, Gumtree, etc, go to bad homes or indeed come from them? Because Collie Dog came via a Gumtree advert, from a lovely cattle farmer who was breeding to get his next pair of working dogs, and most of the litter went to his neighbours as working dogs. Collie Dog is great, was brilliantly raised, we were thoroughly vetted, and he is really well cared for here too!
Yes, Gumtree has some bad people. So does the Kennel Club. Sad but true, some breeders just want the money, or the prestige, or both. Also, rescues are sadly not infallible and can rehome to bad people, who lie very well, or may make a mistake assessing a dog - I am giving one rescue the benefit of the doubt here, but they have made an awful lot of these mistakes tbh...
I advertised our puppies all over the place, vets, pet store, and yes Gumtree. All of the sensible applicants were the ones who found the advert on Gumtree, some after searching for the right dog for over two years. Only one had been looking for a short while - his dog had been PTS due to cancer the same day ours were born 
His new puppy is the absolute centre of his life.
Yes, Gumtree also brought us some questionable types, but it is not difficult to tell someone that they cannot have a puppy if you deem them unsuitable. Free adverts are appealing to people who are selling as they are free, and to buyers as they can indeed look up the seller and search for similar adverts/evidence of dodgy stuff. That is what I did when searching for a pup, I knew I wanted a collie type and I narrowed down the list to those only advertising one litter, as opposed to several.
I did look into going to a recognised breeder, but was appalled by how many dogs they had bred over the years. And that their dogs were kept in outside pens when whelping and rearing, despite being part of the breeder's family...hmm, yes, family pets...
Seriously, please don't discount free ads. Just be sensible and visit unexpectedly about viewing puppies advertised. Find out how much the breeder has invested in this litter, vet bills, food, time, etc. Then calculate how much they are getting per puppy. Are they making more money than they put in? If yes, then walk away. If they won't produce proof of veterinary care, food bills, etc, then walk away. If they hide anything, then walk away. Puppies should never be profitable. Ever. Never ever, ever
Sorry. Rant over. Shall go snuggle with Collie Dog who doesn't know he's been booked in to be neutered and not say anything else on this subject.