Not necessarilly. Depending on the tire design, the tread and carcass of the tire might be nearly an inch thick in places. Also, the screw may very well have gone in at an oblique angle and the OP didn’t say how much of the screw was actually sticking in if it had a tapered head or something.
Furthermore, even if it did puncture, a small nail hole in the tread portion is not going to cause a blowout by itself unless the tire pressure gets low. Yes, you should assume there’s a good chance a tire you pulled a screw out of has a slow leak and so check the pressure frequently, but if it’s not leaking there’s nothing else to worry about.
Since I guess I didn’t really say it, my answer to the OP would be modified (c): Disclose you pulled a screw out of the tire so the buyer knows to keep an eye on it, but I wouldn’t knock anything off the price for that alone.
Part of my quandary is that I’ve had all maintenance done at a dealership which is 30 miles from home (but closer to work), and I frankly didn’t want to go through the hassle of bringing the bike in. And also, frankly, the idea of repair (instead of replace) hadn’t occurred to me.
But I’m resolved, based on your feedback, to do the right thing – I’ve got a potential buyer coming to take a look on Saturday. On Friday I’ll bring it in to a local mechanic and have him take a look at the tire, and repair, replace, whatever is needed to make it safe and allow me to send the buyer off with a clear conscience.
What kind of tires are you putting on your motorcycle?
I’ve cut motorcycle tires apart before. If you’ve got one with ~1000 miles left on it (as in the OP’s case), the tire is more like 3/8" thick at the tread.
The dirt bike and on/off road tires I’ve personally mounted and unmounted seemed to be about an inch thick at the treads. Maybe a little more when they were new, maybe a little less when they were worn out. I would assume street bike tires are thinner, but that’s why I said “depending on the tire design.”