I have bought many MAC pigments all direct from MAC Online so I know they are genuine. My point it though when you see some sellers on E-bay they dont come off a lot cheaper after all said and done, then there is postage and to the unknowing (me for example) there is a huge possiblity that what I would be buying was fake..I doubt I would know. The pitfalls as far as I can see is poor product quality, poor colour payoff, possibly dangerous and untested ingredients which given they are going on sombody's eyes seems a risk not worth taking..Yes it may be a bit cheaper but personally I wouldnt risk it..
I would buy from an MUA who had a good reputation and I have bought quite a bit of Make up from another MUA who buys the most fabulous stuff and has regualr clearouts..She only buys high end stuff and is my kind of girl shopping wise and I have never been dissapointed with my purchases from her which are usually CHANEL.
But back to the main subject , buy from MAC itself..they arent that expensive. I saved my money and bought in bundles of shades and built my collection week by week that way..I did the same with all the MAC eye shadows..I loved it when the mail came and the boxes would arrive..
I have of course seen many many sellers on e-bay selling allsorts of shades by the jar full..entire ranges it seems but they were not any cheaper than buying direct so why risk it..
Remember if it seems too good to be true it usually is.
Andrew