I'll toss out my opinion for what it's worth... We used to have a pro shop - sold tons of stuff... but in the end. A huge hassle and very little if any profit. You are dealing with an industry where the manufacturers have terrible margins, they sell the product them selves on their own web pages, they change makes, models, go out of business, start under new names, have terrible customer service, and on and on and on.
I'm used to retail and internet sales - my scuba shop sells millions of dollars worth of scuba equipment a year, locally in our shop, and more millions on line. So I know about inventory control, have all the systems in place - and when it came down to it.. .the paintball sales was just not worth it. We had a full pro shop at our field, and now I carry just a few feed necks, tank o-rings, and some barrel socks.
It turned out it's just too much hassle for the tiny margins. This is a true and typical scenario:
kid - "Do you have feed necks?"
Me - "Yes, for which gun?"
kid - "An ion."
Me - rummage through a box, pop up with a black feed neck for an ion.
kid - "do you have it in blue?"
me - "let me check...." rummage more..... Find it in blue.
kid - "no, not gloss blue.. do you have dust blue?"
me - "hold on.. I'll look for one...." rummage some more, come up with a dust blue locking feed neck for an ion "here you go..."
kid - "how much"
me - "Tell you what - I'll sell it to you for basically my cost - how about 20 bucks..."
kid - "Oh... well I don't have 20 bucks. I just want to see if you had one... thanks."
Me - realize, that even if the kid would have bought it... I would have made more money selling a slushy to the sweaty kid next to him.
If you decide you want to get into sales... I have boxes of misc stuff I will dump for cheap. Come grab it all... and in there.. there is probably still a dust blue feedneck for an ion.