(a) that's honda for you... not so great. We've been there, done that with our integra. Your really have to try hard to find the right dealer.
(b) if your new accord needed warranty work (?!?!?!?!?????? I thought accords were so reliable), maybe they were trying to make up for it in revenue. Seriously... they have all of your records, and warranty work is the least profitable.
(c) there are places that will do it for free, and you are more than welcome to buy your own scanner/software too. Can't blame them for having a minimum cost to prevent folks from going there, finding what is wrong on sophisticated diagnostic equipment (granted, OBD stuff is not sophisticated), and then going to the local garage and getting it done cheaper.
(d) if a shop is busy, and given that a sensor should only really cost $80-100 (even for an OE one - Honda is really ripping you a new one if they want $400), which means that at best they are making $40 on the part and maybe breaking even on the labor - its justnot worth their time (or your paying for same) to check the seonsor vs. putting in a new one, especially if they know the car has a lot of miles.
(e) a 1998 vehicle with under 100 or 150k ought to have warranty on the emissions system. Shouldnt something like this becovered under that?
JMH