There is money to be made with postcards made by the government, especially the early issues, pre-1900. I think that is because you are dealing with a stronger collector base- stamp collectors. Although most post card collectors do not deal with official postcards, I am sure they do, especially the full front issues.
The key to making money is research, research, research and when you are done... research some more. The more time you spend researching, the more money you will make. I just bought 3,500 postcards for $90 and have made over $400 off of those postcards so far and I'm not even done with them. Some of the postcards sold for $20 or more and one sold for $67. Yes, that was for ONE postcard. If you research on eBay, you will find that there is a lot more to be made on postcards then you may expect. It just takes a lot of time researching and finding out what collectors are looking for. I also suggest buying a nice postcard guide book. I just got one that was a great resource for finding out the values of postcards and how to identify popular postcards. Oh, and if I haven't mentioned it yet, be sure to do some research.;)