do an internet search for finger tip rest & curl palm, with the gimick in figertip rest pick up there coin between finger and thumb and drop it in your other hand, in reality retaining there coin and letting the gimick fall into your other hand.
drop the dirty hand to your side while you talk about telling wether a coin is fake or not and move the coin to finger tip rest / lower curl palm and take the coin with both hands on its lower edge, when done simply repeat the switch but this time into there hand simples.
I belive this is also called the bobo swich, the drop switch and the gravity well palm, in the classic french drop vanish the coin naturaly falls into this position and with practise you will be able to exchange coins by allowing both coins to roll down your fingers without the need to repositon it.
try taking a coin between first two fingers and thumb and dropping it into you other hand, feel how it rolls down your fingers, essentialy thats all your doing ecept your retaining one coin and letting the other fall.
if you want to make life dificult for yourself classic palm the gimmick, take the coin from them and do a classic palm switch, you will feel far superior but the end result is the same to the spectator so save that slight for when you need it later.
a copy of bobo's modern coin magic may be of help in the future. 
