Here you'll find:
- many collectors only
- many who mostly collect and sell off extras
- a handful of full time dealers
- some who are looking to invest money in cards
- some who think that "invest" is a dirty word here(because cards are intangible assets or how increasing values causes them to spend more money)
As far as being an inspiring vintage dealer: the rising values of the last 12 months have made it seem easier than it normally is. If you're selling on ebay, then between their fees and taxes, you're giving up almost 20% off the top to both buy and sell the same product.
That makes focusing on forum transactions much better for the bottom line, but of course you only a reach a small fraction of potential buyers (compared to those places like ebay/amazon/etc.)
So the best answer may be: there is no clear choice
Just have to figure out which venues and practices work best for your particular situation