Setting up to be a 50s - 70s dealer

[mid50sbaseball]

I've been working on starting up something similar focusing on (as my username would suggest) mid 50's baseball cards. I have been picking up several lots on ebay but I'm pretty new at it so I really have no basis of comparison to know whether or not what I'm paying is "good" nor for that matter do I really know for sure whether or not what I am trying to sell stuff for is good, lol. So if anyone has any pointers for a newbie who's trying to get a foot in the door it would be greatly appreciated. I've been collecting off and on for about as long as I can remember and have dallied a bit here in there in buying and selling but this is my first foray into really trying to do it in an organized sort of business minded approach and I'm kinda winging it as I go.