I am selling a high-end laptop on an online auction. It was used for
about 20 hours. I listed all the specs I could in the ad. I want to
include a statement to the buyer to the effect that "I affirm that all
specs used to describe this computer are correct according to my best
effort according to manufacturer." This is simply because the computer
is so sophisticated, and there are about 50 different specs, I don't
want to be accused of misrepresentation in case I included a number or
letter that was wrong (i.e., superharddrive HDx439AA). Good idea?

Manufacturers actually put wording into their ads and specification
lists to protect themselves. "Not responsible for typographical
errors" and "Specifications are provided by the manufacturer" or
similar wording should cover it.

You really don't want to go all out with affirming. I've read a ton of
ads which say, essentially or literally, "I have tried my best to be
accurate in describing this ______." The most important caveat you can
provide to cover yourself is "Item is sold as-is" or "subject to
manufacturers warranty" or whatever you are offerring.

Be sure to require shipping insurance.

Thanks for your clear, common-sense comment.  It helped a lot!