I've never really had dealers for hard stuff. I mean, Adderall is combined amphetamine salts, which are kind of a hard drug, but I've been prescribed the various amp ADD meds over two years, so I tend to look at the use as hard or soft rather than the drug.
My current dude will let me know when he re-ups sometimes (like today), and ask "do u need any?" but isn't really pushy. He's a pretty legit guy overall and if it's a maybe for a deal that night, he'll actually let you know if he can't come through, unlike a lotta people who just stop answering their phone. I gotta give the guy props.
In high school, a dude I mostly went through my friend to get a hold of (he mostly had weed, but could try to get coke, dope, fake-ass mushrooms, whatever) would sometimes call and leave a voicemail about "I got that 'methazine, you know you want it." but, I think that's the most I've ever dealt with. I've heard from other friends who knew him that some blunts he and a friend's brother would sell would be laced with meth, but I'm not sure how often that would be the case. I think hiding a drug in your cheap blunt instead of offering it would either put you off of his blunts or make you just really wanna buy more blunts instead of inquiring if there was a hidden drug in there you could buy on your own.