As has been mentioned, pretty much all temp guns have the same +/- ratio, they usually say +/-2% or 2ºF whichever is greater. To get one that has a tighter tolerance range, you will probably have to spend somewhere in the 6-700$ range or up. They are great for scanning and making sure things look close to correct, looking for hot and cold spots that are really off, but I do not like relying on them as being dead on accurate for the simple reason that even their own specs tell us that the aren't. This isn't something you need to spend a lot of money on, the common one sold by Reptile Basics will do you just fine for not a lot of money, as will the Pro Exotics models. Do make sure you get one with the laser pointer is something I would recomend.
for the record, I use the PE2
Charlie