I know cops DO use smell as probable cause, but I have a problem with that. The problem I have is...there's no way to prove whether they did actually smell anything or not. All they have to do is SAY they smelled something, even if they didn't, and who could ever prove otherwise? If they say they smelled something, well, then it must be so, right? That's wide open for abuse, and because that's so, it almost certainly IS abused as a reason for probable cause, probably frequently.

If I were a cop, I'd use that all the time -- why use anything else as an excuse when that one isn't proveable either way?

"Why did you search this man's car, officer?"

"Why, I thought I smelled [gunpowder/cannabis/burning crack/whatever], your honor."

"Did you find anything?"

"No, I didn't, your honor, but I sure smelled it!"

"Well then, the search is legal. Good job."

There are no real checks and balances there. There's no way to defend against that, because you can't prove the cop DIDN'T smell what he said he did, and the only proof there is that he did smell what he said he smelled is because he said so. That would be acceptable if cops automatically dropped dead if they lied, but they don't, and in this case there is every incentive to lie, and little incentive to tell the truth.