Spot on JL. I've had gobs of folks contact me, needing help or information on bows they didn't buy through me. I've never refused to help, even though it cost me time, and sometimes money. For one, I try to treat folks the way I'd like to be treated, and two, people remember good service. It always pays me back in the long run.
There's been a few (very rare) occassions that I didn't help with other things--it was when it was obviously an attempted scam. You can be courteous without being stupid.
It's a mix of technicalities vs. realities. Technically, if a warranty is only good for the original purchaser, then technically the bowyer shouldn't be held responsible, regardless if it's his fault or not. Technically, it would be the buyer's responsibility to find out up-front if the warranty was transferrable and/or if the bowyer would honor the warranty for any amount of time if the bow changed hands.
The reality is anyone expects a bow that is 6 months old to hold up. The reality is if you pay top dollar (new or used), you expect top quality, including top service. The reality is the bowyer can save some time and money up front by sticking strictly to the warranty, but loose much more in the long run. The reality is word gets around, good or bad. That is, again, if the problem could be due to materials or workmanship.
Just my opinion, based on several years of owning/operating a traditional archery based business.