I'd say $3k a month is POSSIBLE, but perhaps not probable. It would really depend on how much this guy gets per click vs. how much he spends.
As an affiliate myself (albeit for Amazon), I can tell you that I'm nowhere NEAR that much a month despite a fairly sizeable investment. I'd guess hes spending about $10k a month on it or so if the margins are similar to mine.
I'll hazard a guess that YOU'D like to be making that much a month. I think that while it may be possible to be making that much per month, it would require a significant investment of time and money. I'd suggest starting slow as an affiliate, investing small sums of money at first and making sure you get a positive return on it.
If you have any more questions, StickyMail me.
SideNote: Though I don't have any experience with eBay, my guess is that it's important to link correctly to the appropriate products. If you DO start a side-business like this, be sure you weed out the get-rich-quick eBooks (like the one you seem to have read) by raising the minimum price over $10 (if you can).
I DID see a news story recently that eBay is going to implement UPC input for easier listing. I'd jump in after they do this if you're looking to target individual item keywords on AdWords, as it will probably make the target results a LOT more relevant for people clicking through, and these people are more likely to earn you money when you deliver them relevant landing pages.
[edited by: Shak at 11:38 am (utc) on Sep. 17, 2003]
2nd edit by Brian Ruth (SideNote added and last sentence rewrite)
Obviously I'm bias but I have used adwords to achieve such results.
Ebay currently allows you to link to any page you want with your affiliate ID, even the search results for certain keywords.
It does take time to find keywords, test your ad copy and setup the ads but once they are in place they generate steady recurring profit.
Jeremy
Even if you don't want to promote products selling on ebay, using ebay to find niche markets is a real winning strategy. Everything imaginable is for sale there. If you look hard enough you are bound to find something that isn't too competitive on adwords.
Jeremy