After pinpointing, and just in case it is an old coin, I tend to feel for the coin with my finger, then get the screwdriver under the coin and lever it up to the surface undamaged. If you probe around with the screwdriver too much, there is the chance you can scratch the coin. Also if I have the pinpointer in the hole, and can't quite get a full signal, rather than dig the hole out more, I will probe in from a different angle to try and get closer. Saves you ending up with a big hole with a pile of dirt, which sort of defeats the purpose of using this method in the first place. A lot of coins you can pinpoint from surface running across the target with the pinpointer, and then perpendicular to the target. This makes for more accurate probing, plus indicates the rough depth of the target (if pinpointer can detect it, it is ususally only a few inchs deep).
Also wear gloves, in case there are any buried sharps. Get some thin cut resistant ones, so you still have some decent feeling when locating objects (bulky riggers gloves are a pain).