Digging this up, as I have some numbers and facts.
1- Started selling comics, online, in 2007. To date, I've sold 847 comics via eBay and 1,043 in person via Craigslist.
2- Tough to get exact numbers, since my eBay totals include random junk, but I can safely estimate about $1,500 total profit from the comics sold strictly on eBay.
3- Craigslist was good for bulk, as I sold a higher quantity, there, but only $481 in profit.
I still have yet to put a dent into my stock. The key thing is: EIGHT YEARS and I'm still trying to sell this stuff. It's not that they're "worthless", since I've sold some absolute garbage for more than something I thought was valuable (I've made more money off of Muppet Babies than I have off of X-men). Most expensive single comic I've sold, online,-- "Adventures of Super Mario Brothers #1" for 25.99.
The problem is moving the overall BULK. It takes a long time, as nobody wants to dish out a large chunk of change for a huge collection. People want "deals"...so while it might be a better deal to buy a ton of stuff in bulk, most folks would rather nickel n' dime and pay 25 cents to 5 bucks for individual issues.
I think that's part of the hobby, though-- the actual "collecting". For instance, if you were to buy EVERY issue of Avengers, for $1,000 (which would include the key issues of #1 and #4), where's the fun in that? You're instantly done.
It took me about 30 years to complete my Avengers run. Did I have fun? Yeah. Would I do it again? Hell no.