[Warning: I'm not a lawyer.] As people answered it mostly for USA, I gave it a check for other countries.

For both Italian law (article 640 of the Penal Code) and Brazilian law (the famous article 171 of the Penal Code), this behaviour falls neatly into fraud laws, and leads to a few years of reclusion. I couldn't find any law specifically for selling it as if it was a drug though.

For Portugal I actually found a paper about the topic. It claims that it isn't a crime per se, but it's usually filled under other crimes, and the paper proposes the creation of specific laws against it.

I kind of expect other countries and their legal systems to be the same in this regard. It's simply not a pressing issue.

I used to have this friend we called Blaster Taylor. He was cool as fuck until he started abusing Adderall, and that Adderall addiction turned into meth pretty quick. Started shooting it, that's when I stopped kickin it with him.

Anyway a couple years after that he got busted selling a bag of rock salt to an undercover cop saying it was meth, and he did a couple years for that as I recall. I don't talk to any of those dudes anymore but last I heard he's out by now, complete with swastika face tats.

To paraphrase John Darnielle, selling fake meth was a bad idea; but selling it to a cop was a worse one.

Yes. Selling something advertised as a prohibited product, whether or not it's true, is technically a crime. Assuming we're talking about the US, in most jurisdictions this would be treated just about the same as if you were actually selling the same volume of the advertised product. I believe the reasoning behind it is that even if it's fake, you're creating a market for the real product to be traded, or something like that.

So if you sell a 1 lb bag of flour calling it cocaine, you'd get charged as if you sold 1 lb of coke. The final judgement may not be as severe as actually selling a pound of coke, but the initial charges typically will be.

Also, flour and sugar do not look like coke or meth up close. It would be immediately obvious a user/seller the moment it's in their hands, so this is also a really good way to get your ass kicked.

Continuous Integration?

A) Flour

B) Fraud

One Google search later,

Selling counterfeit illicit drugs is illegal even if the substances used to make the imitation drug are not illegal on themselves

I suppose it is fraud. If they do hurt themselves after trying to consume they might end up in an ER and a hospital might be required to report (even if user would not have for obvious reasons)

What kind of flowers are we talking about?

CI? Criminal Informant?

If you're law enforcement or part of the DoC, you probably have better places to ask. I you're caught in an undercover sting, you can talk with a public attorney at the very least. eitherway, there's more reliable sources of information.

You can get arrested, you could be detained under a reasonable articulable suspicion of having committed a crime.

As to whether or not that would ultimately lead to trouble? No. Could it still cost you money, time, etc? Yes.

Depends on the state. I imagine over the years, enterprising drug dealers have done just that to dupe unsuspecting buyers. It wouldn't be far fetched that a state would write laws to capture just such an instance.