I agree with you, Dominique33. It really depends on the Sephora store.
There is one I don't go to anymore because the people working there are just rude, and very unhelpful. Plus the testers are in such horrible condition.
The Sephora closest to where I live have some of the kindest and nicest sellers ever, and everything is clean and neat.
Horror story (at least for me, lol) was on wednesday. It was the first day of sales, and I saw 3 Guerlain Rouges G on sales. The testers were right there, but one customer opened the lipstick and swatched it on her hand. I told her with a smile that there were testers right there; she gave me nasty look then ignored me. I quietly notified one seller (who was horrified) who quickly went to offer her advice and help, just to check she wouldn't do it again.
Anyway, back to the topic.
I have been stalked not so much by the sellers but more by the security guards at the Sephora I don't go to anymore. They followed me. I like big bags, and pockets on my clothes. I browse through counters, and I like to swatch. I often go out make-up free, in jeans, t-shirt and ballerinas or tennis shoes. I also look younger than I am, and I like luxury make-up. So I must look like a teenager who doesn't know anything about make-up and who doesn't have enough money to buy make-up sold at Sephora. So I guess I look suspicious and worth following around. It's super annoying.
I don't mind being asked "Hello, can I help you with anything?" / "Hi, do you need advice?" but 4-5 times in a row is annoying.
One bad experience that I had was at the Guerlain counter in Le Printemps. I was admiring their wall of Rouges G (I have a weakness for those). The seller looked at me with spite, like I had no business looking at such expensive and classy items in my cheap clothes and make-up free face. I felt humiliated.