I've always been fond of warped tape sound - it's a feature of the medium. Instead of dismissing the whole package as damaged beyond interest, I usually try to embrace the phenomena in some way if I encounter it. Certainly there are times when it'd be nice to have the option to hear the original recording unaffected. In my experience cassette tapes from the Balinese ANEKA label (a scruffy, slightly awkward alternative to the mighty Bali Record) seem to be afflicted about half the time with some sort of warped weirdness. The cassette pictured above (from which this short gilak tune comes from) is a good example - the entire B side is empty, while the A side warbles throughout. You can also see that the little pressure pad thingy that sits under the tape has become dislodged and free floating - that being a simple fix. Once the tape is stretched though it's warble city all the way. I usually ask the vendor to "test" the tape before purchasing - they don't mind, they know the drill - it's the final quality control check before the thing heads out into the world to be forgotten or repeat itself until it dies.