Did he also say it was rare? I love that one. Perfectly serviceable bike not horrible at $20 but unless there is some sentimental attachment, like you had one when you were 8, there are better bikes out there and at this time of the year and with the way the vintage market appears to be going there are deals to be had. Be persistent patient and picky then you can spend the winter refurbing your find. Good luck.
As an example I waited this one out on CL it was priced to sell but languished. I threw out a $25 offer in week 3 of the ad and it was accepted. 1988ish Novara Ponderosa, house brand of REI, Japanese built steel MTB, full Shimano Deore drive train. The paint is in rough shape but the indexed Shimano Deore thumb shifters are worth the $25 just by themselves....Removing the book rest (it was a trainer bike) the bull horns and replacing the grips will improve the look significantly. IMHO,