I got both my cats at a pet store, because I didn't know any better at the time.
Elly was the only female cat left, she was snoozing with mum, so I figured she looked like a nice quiet cat. Boy was I wrong.
Marlee - a year later - was also the only female cat left. Funny looking little white thing with a big black stripe on her head. She looked very small, and in hindsight I think she was younger than the regulation 6 weeks. She was quite timid for a while and she is still a little neurotic, sometimes it's like she's completely scared of me even though she usually follows me everywhere and loves to sit on my lap. She also frequently paws soft things like jumpers, exactly the same way as a kitten paws their mothers tummy to push the milk out. I saw a show on TV recently that said that kittens that are removed from their mother before about 7-8 weeks will often behave like this for life. The good thing is that she is really happy when she does this, she's purring loudly and her eyes are closed.
Marlee obviously has some siamese in her which explains some of the moods, but I think the pet shop environment and early removal from her mother has probably had a big effect on her.
Next cat will be a teenager or young adult from a cat shelter, I am never buying from a pet shop again.