As with all price guides, this won't be perfect. I do have a few particular quibbles in particular. In my opinion the kit market as a whole is down somewhat, given the general economic times as a whole there aren't as many buyers out there for high dollar kits, thus lower prices.
More specifically, I do feel the price on a Metal Slug kit is too high. I got a steal of a deal at 75 bucks for a NOS kit, so as mint as mint gets on eBay. Then when I wanted to sell it, I couldn't get more than 110 for it. I'd say 175 on the high side is more reasonable, 100 on the low side.
I have never heard of Last Blade 2 selling for numbers like that. I sold mine to Rot for 400 bucks. I bought it for 300-350 if I remember right. Maybe you have more info than I've seen but that game rarely changes hands.
Breaker's Revenge is extremely high as well. It is an extremely rare kit but the last one that was sold in the forums was listed at less than or around 300. Sure it sold in an instant but that doesn't justify 700+.
NAM-1975 is a kit that should be listed as R just like anything else from 1990-1991 or so. Those kits are old at a time when the MVS system was truly an operator only system, few are around. The prices are ok, I bought a Nam for around 100, but I sold it for around the same, there isn't much demand out there for it compared to the flashier 1996-1999 games.
Garou is too high, 300 tops. There are just a ton that are difficult to get but not commanding the kind of prices you have set them at. Sure offering 2k for a Last Blade 2 might get you one, but if it comes up for sale on the forum or in an auction, I doubt it is going to see more than 600.
Like I said though, if you have more specific info, let's hear it.