It's no secret market leaders like MAC, Bobbi Brown and Urban Decay have knock-off/ sub-par counterfeits springing up online through mediums like eBay, strawberry net, ect . Some may also remember Target Australia selling counterfeit MAC a few years ago, and the huge lawsuit that followed.
Anyway, the danger is in what these knock offs actually contain. With no governing body controlling what is put into these products, or the methods of production, there is the potential for serious damage to be caused to the consumer. Having samples of these counterfeit products testing positive for lead, and high levels of talc, and other heavy metals not safe on the skin, or for human consumption. Knowing many counterfeit products are more often then not produced in third world factories, the reality check being , they may have no hygiene practice in place meaning, there is the potential use of unfiltered, bacteria ridden or contaminated water used as the base of your foundation, hair care or makeup.
With the use of these cheaper products/ lower standards of hygiene, lowering the cost of production, hence making the cheaper sale price online. Inclining the average consumer to choose an online third party seller over the official company website or in store.
Another potential problem posed from unofficial resellers is the sale of product past it's expiration date. This is a little easier to spot as it's often "special edition" ranges / colours, change on formula consistency ( separation) and smell. Unfortunately consumers cannot see these until it's already too late. Out of date products are also vulnerable to harmful bacteria build up.
From a makeup artists perspective, the potential that I could harm and damage my clients is completely unethical and dangerous, and in to way justifiable financially. In saying this I buy all my product directly from the brands official manufacturers, and keep proof of purchase for all high end/ professional quality products stocked in my kit for my own piece of mind.
I know budget can be a big issue for young people on particular when it comes to high end cosmetics or cult classics, especially in Australia with the consumer markup on cosmetics and beauty products. If this is the case, I recommend looking up "dupes" for the specific product your after and buying a similar product from another brand ( mac vs. rimmel), Or spending that extra $$$ on the original product, your faces are to precious to end up with permanent scarring or other inflammatory symptoms / infections.
Play safe!