What breed(s) are you interested in? Because, honestly, if your entire dog experience has been with one Goldendoodle, the "larger" Russian dog breeds that I can think of, namely the Black Russian Terrier, Eastern European Shepherd, and the various Ovcharka are not ones I would recommend. Even for experienced dog people, they can be a challenge.
As far as your last statement, yes, bitches will sometimes lose a litter after being confirmed pregnant, and yes, sometimes a breeding won't take. Sometimes, the litter is lost for other reasons. A friend of mine had a bitch confirmed in whelp to a very good male, only to wind up spaying the bitch halfway through gestation in order to save her life after she developed complications.
Honestly, if a breeder is so "hungry" that they will sell a puppy to any Tom, Dick, or Harry who is willing to fork over the money, no questions asked, that's a breeder I'm not interested in. Good breeders care about where their puppies go, and if your first contact with them is "I'd like to order XYZ, give me a call", then the odds of them doing anything more than just hitting the delete button are pretty slim.
As far as your last statement, yes, bitches will sometimes lose a litter after being confirmed pregnant, and yes, sometimes a breeding won't take. Sometimes, the litter is lost for other reasons. A friend of mine had a bitch confirmed in whelp to a very good male, only to wind up spaying the bitch halfway through gestation in order to save her life after she developed complications.