It's so funny to see that apparently so many people think or "pretend" to know what they are dealing with, but in reality they have absolutely no clue and their claims are baseless:
1.) M. Kozacek is 100% correct. It is indeed a 1992 Klein Attitude bike.
2.) If it's a "true" 1992 Klein Attitude or not, well that I cannot say, but I assume yes, since I think the seller simply is not informed enough about Kleins in general and that beside that he seems to be honest in his claim that it's an original (genuine Klein Attitude).
3.) 1990/ 1991 Klein Attitudes had a boxed fork and the downtube Klein lettering was black in full...
it is much more difficult to distinguish a 1990 Attitude from a 1991 Attitude, altough as M Kozacek pointed to you can see the difference also in the plastic cap (headset): 1990 Klein Attitudes had "Klein" written on the seal.
4.) For education purposes: You can watch/check for yourself if you go to www.wundel.com
and click on "classic Kleins" there you will find all the major Klein models and from all years....
You can compare 1990 Klein Attitudes with 1991, 1991 with 1992 and so on...
another site is www.mtb-kataloge.de
you can find almost all brands, including Kleins and see for yourself.
5.) Last but not least, I would like to say something encouraging on the behalf of the seller:
If the bike is truly an original - and it REALLY looks that way and yes even if it's from 1992 - then with it's very nice condition the price is FAIR.
Best regards to all,
"KLEIN, NOTHING ELSE EVEN COMPARES"