The product 100% sold by Helena Rubinstein's counter must be genuine. Rest assured, Tmall flagship store should have no fakes;
You can also try it when you buy it at the counter, and you can see the real thing. I didn't see the real thing in Tmall flagship store, and I don't know the shelf life of the product. I don't feel at ease to buy it at the counter.
Tmall flagship stores sometimes hold activities, which may be more affordable than offline counters.