Last time I checked, Mary Kay was a member of the Direct Selling Association, which is a watchdog group for network marketing companies. Only about 200 companies out of the 5000+ are invited in, after a year of their books being scrutinized, their compensation plan reviewed, distributors interviewed, etc. People throw out terms like "pyramid scheme" but those are illegal! Any company that trades on the major stock exchanges has open books.
There are fewer "layers" or levels in most MLMs than in most corporations, so there is a lot less tacking on of fees to support a whole ton of people. So products aren't marked up as much in most MLMs (at least the good ones) as in most stores. They are badmouthed by corporations who compete with them, but it's not based on anything concrete, assuming of course that it's a good network marketing company. But that's no different than wanting to patronize a good store, see a good movie, go to a good restaurant. Just because a few are bad doesn't mean you write off the entire category.
Are you making a commission on what your downline sells? Of course! But how is that different from the CEO, senior VPs, middle management, janitors, secretaries, human resources personnel, and payroll staff at Target's headquarters (or Hallmark's, or Staples', or IBM) making salary on what other people are selling in the stores? It's not. In fact, you're paying fewer people in network marketing than in all those mega-corporations. You just don't see it with corporate America.
If a company has been around for a long time, they're doing something right. Look at distributor loyalty/longevity, and look at monthly order requirements/quotas. Look at the downline structure - if you can only sign up 2 people and then they have to sign up the next batch (a binary structure), you'll never make any money. But if you ran a store or a car dealership or a sandwich place, you'd only make money if you had enough salespeople selling enough product every day.
A cosmetics company has the plus of selling a consumable product - it gets used up so people want to buy more. That's good. What makes it tough is you can only sell to women, and within that group to women who wear make-up or at least use a lot of skin creams. You almost have to work with people in your area (so you can match the shade of their skin or let them physically try products) so it's hard to build a nationwide or worldwide customer base. If someone moves, they remain your customer though, but you aren't going to run webinars or anything else to get new people in other states. So your market is limited .
You don't have to harass friends! That's really not allowed in the Direct Selling Association, so companies that encourage that get booted out of the DSA. There are always a few salespeople who slip through the cracks and do something unethical, but they don't make money.
Look into whether the starter kit is fixed, or whether you can buy different things than the next salesperson. That's a good sign. Look into monthly minimums - that's a bad sign. Look into the start up costs. Is there a business guarantee (such as a 90% buyback within 1 year)? That's the sign of an excellent company.
You have to love what you're doing, you have to be a fun and go-to person who really listens to customers and isn't trying to force something on them to make a monthly quota, and you have to put a ton of time into it just like any other job. Only you can decide if it's right for you.