That pretty much confirms that no testing was done. Testing costs hundreds of dollars, breeders who have taken the proper care and testing usually charge at least $500.
Don't take this the wrong way, but 300 dollars is not very much at all when it comes to caring for a living animal. How are you going to afford his care if something happens? Most vets charge 50-85 dollars just to walk in the door. Vaccines cost around 20 bucks and since he is young he will have several of those done this year. Spaying or neutering costs around 200-300 dollars, 30-50 dollars a month on food, wee wee pads every week, $15 leash, $20 harness, puppy training classes, etc. That 300 will be gone in the blink of an eye.
Also, there are low cost clinics BUT those are generally for people who are down on their luck and fell on hard times. Do NOT get a puppy if a low cost clinic is all you can afford.