Hundreds of animals are brought to veterinary practices every year, by the RSPCA, the Police and members of the public. Some are completely healthy! Others are sick or injured. Pets without ID are stray. Strays animals, where possible are rehomed, or alternative difficult decisions have to be made based on age, injury, and health.
Microchipping is compulsory in dogs by 8 weeks of age. The breeder should already had them microchipped and passed on all relevant documentation to you so you can transfer ownership into your details. This must be done as soon as you have taken ownership of your new puppy.