There aren't a lot of relievers who would be obvious upgrades for the Giants, and there are about 18 or 19 teams chasing the ones who are.
Back in 2012, the Giants needed a second baseman. Freddy Sanchez was hurt and Emmanuel Burriss and Ryan Theriot were, wait for it, not hitting that well. Everyone knew the Giants needed a second baseman. Everyone knew they were going to get one.
Not a problem! They traded for one. There were plenty available, from Hanley Ramirez to Omar Infante, and not a lot of competition. They were able to snatch a perfectly competent Marco Scutaro from a division rival, giving up a prospect out of their top 20 because the competition was so mellow.