my parents have been byb of goldies for 30 years, only have one bitch at a time though, so probably have had 7 or so litters in that time?
First two litters from their own dog, a beautiful handsome boy who came from a "professional breeder" (ie a puppy farm) with a smart pedigree and great conformation. He was a little highly strung, but made gorgeous pups. At age 5-6, he got out the house and ripped apart a small pomeranian down the road. Foolishly, my parents kept him. 6-7 months later, he attacked a child. He was PTS the same day.
So you cannot necessarily tell who is good and who is a bad breeder. But there were two litters out there with his genes and temperament. The bitch was as gentle as can be, so hopefully none of his progeny went on to be highly strung. BUt how can you tell if you dont have lineage/breed history? Have you checked out her litter mate's scores, seen whether or not any of them have done well in the show ring or on the gundog circuit? Have you checked with the breeder, to see if any health issues have come up in their line?
I would concur with others that 6 is too old for breeding. Especially if you haven't had all the tests done. We considered breeding our own 2yo goldie, but as her hip scores were less than optimum, and she is not a working dog where hip scores are secondary, we decided to have her spayed. No point in perpetuating dodgy hips, no matter how wonderful the animal.
From our research, the breed standard says that hip score up to 50 are ok, I believe, but really you want hip scores much, MUCH lower. Working gundogs are usually in the 20s, show dogs are usually single digits or early teens. CHeck out her litter mate scores - I think the kennel club has them online - and see how they scored.
Hip scores should be done at about a year, so their hips are in their prime condition. By 6, she'll have some wear and tear, especially if she is an active girl. People looking for a good retriever will look at her scores and make decisions based on those numbers - we would never choose a pup from a dam with poor hip scores, having had a retriever with bad hips and seen her suffer in older age.
Please think carefully about what you are doing and do it for the best reasons.