You don't need film backing paper to experiment with the counter. Just use any kind of continuous paper, like cash register receipt paper or butcher paper, etc. You can tape it onto an empty spool. My own Yashica-D has sort of high pressure on the film counter wheel that pushes against the film. Every roll I develop from that camera has little tooth marks visible on the margins of the film strip. The little grippy wheel doesn't actually pierce the backing paper, but the little track is obvious. The film counter gear track allows me to distinguish negatives taken with the Yashica from my other 120 cameras.
A dirty screen falls within "working, as is". A non-operational film counter might, under the minimal standards of ebay, fall in that category as well.
But a film winder that doesn't work means the camera isn't "working". So if the suggestions in these responses don't work, contact the seller and let him know his description is not accurate and that you will leave objective negative feedback to that effect. He might offer some settlement but, more importantly, he'll be penalized to some small degree (by negative feedback) for misrepresenting his item.