I never charge a motorcycle battery at more than 1 amp. You can safely leave it on a 1 amp charger for 24 hours. As someone said, not all batteries work right with those battery maintainers. But if the battery is charged, or has been on the charger long enough, and still won't start the bike, there is a problem. If you can jumpstart the bike, then the battery is bad.
I won't spend more on a bike than I think it's worth, but if it's a good deal, I don't seem to have a problem buying bikes I don't need.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped