good idea with the sets Nicoletta,
the problem i have with performing with known friends and especially at school compared to the street is that they see you as an equal not like a person on a different level where they might think twice before e.g. reaching into your pocket and pulling out a ditched coin or grabbing the cards and shuffling themselves. Of course it would probably be different if performing for older friends, but I still prefer performing for the unknown
I used to have the same problem, but i found recently (this week lol) that if you somewhat condition your class mates into not needing to examine your props, theyll stop doing it! What i mean is do some tricks where you end completely clean, wheather theyre card tricks or whatever, do those for a little bit and then let them examine your props after. for example this week i did a LOT of scotch and soda. and afterwards id stand up, shake myself out let them examine the coin let them examine my coin purse to look for the centavo, and when they find nothing, theyre amazed. that was on monday, i performed in that class for id say at least a good ten minutes every day this week, not once did they even ask to examine my stuff. its great! idk if thats what did it but its something you guys can at least try out.