Whilst I was at a car boot sale last year I walked past a makeup stand. Being a beauty blogger & all round makeup obsessor (& hoarder) I had to go over. To my surprise I noticed a stand full of "MAC products". Because I didn't know that much about makeup at the time, I was stood there debating for well over ten minutes on whether they were real or fake. My gut told me they were fake - who sells MAC blushes at £5 each? - but I didn't know for sure. I ended up buying one and did a lot of Googling & came to the conclusion that it was fake. I didn't know the 'warning signs' as they call them and so I wasted money. These are the ways that I found how it was counterfeit.
I'd never bought a MAC blush before I bought the fake one so I didn't notice that the font on the front of the product was much thicker than the genuine one. This is a key thing to look for - the real MAC products have a much thinner font.
This is only really comparable and noticable when you have them side by side. The fake blush (pink one) has a grittier texture and much more powdery looking than the real one (brown). Although on this photo the brown does look questionable - that's what happens when you use a brush with translucent powder on to apply it!
My fake blush came with a mirror. Again, I didn't own a real MAC blush at the time and so I couldn't figure out whether the real ones come with a mirror. They don't. If you find a 'MAC' blush with a mirror and/or a brush, it's a fake.
This is by far the most obvious way to distinguish between real and fake. As you can see, the real one has a name and the fake is just called 'powder blush'. The fake also doesn't have the type of blush it is and the font is in white bold. No MAC blushes will ever be named with a number!