What to look for when buying an older dog off an advert?

I’ve never owned a dog before, I did have a little job of walking peoples dog’s for money that included pups, The dog I found is on preloved.co.uk it’s a 7 yr old Sheltie that they are giving away for free as they bought this dog from a rescue centre and apparently some of their family are allergic to the dog (I have asked about the dogs temperament and whether the dogs in need of basic training) say if I went to meet this dog what should I look out for and what else should I ask the owner about?

And is it a good idea for my first dog to be from a rescue centre because from past experiences visiting my local Dogs home some of the dog’s are quite damaged from past life
@Verulam that was the first plan but I asked at the dogs home in Manchester where I live and they were of no help they had no idea about the dogs temperaments and they weren’t even sure if we would be able to stroke them..
Wise words Nishan
I messaged the owner asking what the dogs temperament is like and whether she needs basic training and their response was ‘shes fine round new people’ I’ll give it a miss this time thanks for the help everyone to the dog shelter it is!

How can you tell a dog’s age?

My husband and I have a rescue dog, a dachshund, and we have only a general idea of his age. My husband adores this dog, a dachshund, and he is afraid that he is older than we have estimated (we are thinking about 7 or 8). Is there a way to tell a dog’s true age? Can a vet tell? My husband is afraid he may be older than we think, and dachshunds usually only live to be about 12-14.
Tartar on teeth: He lost his two front teeth, but other than that, his teeth seem fine.
Graying on face: His bottom jaw is very gray now, other than that, only a sprinkling of gray.

do all pet stores get their dog’s from puppy mills?

I’m getting a puppy soon (mini schnauzer) at a pet store that seems like they take care of the dogs really well, but I’m hearing from ppl that those dog’s were bought from puppy mills…
Is it bad to buy the puppy there?