Generally, I say no. There are too many fakes to take the risk and many sellers have great feedback as people are unable to spot the fakes. I was once a victim to fake Bobbi Brown foundation and was left with a rash that took weeks to clear. I took all these from ebay today - all fake.
These are just two I found on the first page when searching "Bobbi Brown"
In this pic you can clearly see the packaging is not the same - the real has two lines of bold text and a slightly different shape. Always check the real products image on the website first - it is easy to check whether a brand has recently changed packaging too - just google it!

These brushes are fake - there is no "luxury brush set" brand from BobbiBrown - the case is wrong and they are not the same brushes.

So buyer beware! Fakes may seem harmless but you don't know what is in them, if they have been tested properly or any information. Remember - you only have one face!