1) If you told them what to do several times and the spec still doesnt follow your instructions...just pack it up and leave. Tell them that if they wanna get entertained, they better listen to you. You dont want to put them down in anyway, you just wanna make sure that they know you are in control so maybe next time, dont be be a jerk.
2) This is tough one. There are several things you can do to avoid this situation.
-First, polish your DL !!! I dunno how comfortable you are with the sleight but many people claim that their DL is fine, but in reality, it is quite crummy. Your DL should look no different as if you are lifting 1 card.
-Second, the human minds are weak. It can only concentrate on one thing. After you give them the card, if you quickly move on with the trick, people will focus on what you're doing next instead of the card they are holding. If you just give them the card and hesitate for a second or so, the specs will have time to think about what happened.
-Also, if you wanna be really safe. Ask your spec to hold their hand out, put the card on their hand and keep a finger on it. Then tell another spec to put their hand on it to cover the card. This is a good way because the other spec is the one helping u cover up.
If the worse did happen and they ask you if they can flip over the card. If I'm doing like the 2 card monte or the ultimate transpo...Ill say its a memory test and peeking is cheating.
If that line wont help the trick you are doing then ignore it and move on immediately. Just misdirect them and move on. When they need to catch on to what you are doing, theyre not gonna have time to rethink.
Hope this Help