Your "Molly" is made by one of three types of people, all three yield a different quality product.
1. Rc supplier, This "Molly" isn't Molly at all. Because of all the information on the Internet and the majority of drug users ignorance of this information research chemicals have started to see their way onto the ecstasy/rave scene. And what's worse is most people don't even know. Getting a test kit will help you identify this type of molly. Most of the time the person selling this is someone who found out about this "replacement ecstasy" you can get for dirt cheap on the Internet and it makes you roll. A close (at the time) friend of mine was selling Molly for a year, he gave it to me once for free and I took it, thought it was good but not great, but at least I was getting "cleaner" stuff than I would be getting in pills (that's a huge myth by the way). I wanted some for a rave and this time I had a test kit, he had "two Batches" I said whatever give me .5 of each. They were methylone and butylone. He legitimately didn't know what it was, I watched him call his hook out for ripping him off for so long. And you know what he did? Found his own site and kept selling fake Molly. Moral of that story is get a testing kit and use it, even if your friend sold it to you. Most people selling rcs wont let you test it before you get it.
2. Tweaker chemists, they all know about this site, a lot of them post here.

Note: you don't necesarily have to be a tweaker, but it helps): anyway these are ammatuer chemists who get spun and read about drugs on the Internet while taking Ochem classes at community college. You'd be surprised what you can make with limited resources and a semester or two of Ochem under your belt. Because of their chemistry backround they know what cuts they can get away with and how much to use down to the miligram. Some "tweaker chemists" actually make really good stuff, but just as many of them cut their product with as much cut as they can possibly use without failing a test. MDMA synth is really difficult, you need to really know your shit to pull it off and understand the chemistry, but the information is available. But there are plenty of other synths that are much cheaper and easier (meth, most rc's, other obscure yet illegal drugs). Cheaper + easier = more money in less time and tweaker = shady. Now not everyone who synths in their kitchen cuts their stuff, like I said they can make really good shit if they do it right and they give you pure stuff. This is the vast majority of legit street Molly.
3. The mass producers, these people are involved in organized crime whether it be the mafia or the cartels. They mostly make their MDMA to press into epills but for whatever reason a small percent of pure (which is generally literally as close to pure as possible) is diverted to well connected people, where 90% of the time it's stepped on at which point it becomes no better than kitchen chemist stuff. If you happen to be lucky enough to get some of that 10% that hasn't been cut you shouldn't ever fuck with the person who sold it to you, ever, because he picks up directly from and is well liked by a crime syndicate. This is the least common type.
Depending on where you live and who you know one type may be more available to you than the other.
Well chances are you don't pick up from a chemist, you pick up from a dealer who you've probably grown up with and isn't too far into the shady part of the drug world (yet). But that's where your drugs come from. Why did I tell you this? So I can tell you this.
Here's a few pointers on how to tell how legit your shit is.
A few red flags:
1. It's a powder or a lot of tiny crystals, the only reason someone would do this is to cut it. When synthed MDMA is shards, no matter what your dealer tells you or your dealer tells him. The shards should look like small shiny grains of rice. Ever seen meth? Cause that's what it should look like.
2. It's sold in gel caps. Most legit Molly is sold by weight.
3. It fails a test. I don't need to explain that one.
4. You're told to only snort it. MDMA is MDMA is MDMA and it's active orally.
5. You're getting a really good deal. If it seems too good to be true it probably is.
A few good signs
1. The bigger the better. Although it can be cut by the chemist before it's made into hcl salt, large shards are an indication that it wasn't stepped on after the synth. It can be recrystalized but it's not worth it for most dealers to do because most consumers will buy it anyway.
2. Instant reaction. when tested the amount of time it takes for you to see a reaction can be an indicator of how pure it is.
3. My own test. This tests for a lot (not all) of cuts used with Molly. Put your Molly on foil, heat it underneath with a lighter gently until it melts and boils. Heat gently until it evaporates. There should be a very faint yellow/light brown residue left on the foil, there shouldn't be a lot of residue. Ever smoked meth off of foil? That's what it should look like. If the residue is black or there is lots of it chances are it's cut, cause Molly doesn't do that. Even if you heat it too fast and burn it there's barely any residue on the foil. Good for showing innactive cuts. DO NOT SMOKE IT.
4. It's not cheap, quality over quantity, always. Cheap Molly can be sold at a high price, legit Molly can't be sold at a low price. There's exceptions to this but the best Molly I've ever seen has cost me almost twice as much as I paid for shitty Molly.
Always test your stuff and never trust your dealer or some idiot at a rave, hell don't even trust me. I know this because I've seen it and I trust my eyes, why the hell should you trust my eyes.