Internet bargain or scam?

Yes. The problem is you don't know which until you check them out. We have had some very happy clients who purchased over the internet - and some very upset ones.
In one instance, the client received an appraisal which failed to clearly state that they were buying a clarity-enhanced (fracture-filled) diamond, and the value stated was three times higher than what was paid. The NGL appraisal placed the retail value close to what was paid with prominent disclosure of the enhancement process. On the other hand, we have verified many great purchases, especially when GIA or AGS was the certifying lab and everything checked out.
We have also seen a lot of misleading colored stone transactions on-line. The biggest area seems to be in the emerald market, where stones too light to pass as emerald are being sold as "Colombian emerald". True, they may be Colombian in origin, but cannot be gemologially classified as emerald if not at least medium-light in tone. On the other hand, many colored stones bought on-line price out significantly more than their transaction price - but remember, price is not the most important factor anyway. The best advice is to obtain a guaranteed refund if not satisfied.