Thanks for the responses, folks. Technically, the buyer didn't request the survey, but he wants to know where the lot lines are when he walks the property. A survey is the only way I know to accomplish this with certainty. The neighboring property has a bunch of tires and other trash piled up near, and possibly over, the line, so I can see wanting to know exactly where the boundary is.
@Matthew Deines - I thought about splitting the cost with him. $1500 beats $3000, but I'm still not sure it's worth it with no guarantee.
@David W. - It's a 10 acre parcel that hasn't been platted in 50-60 years. The $3000 is a ballpark estimate from the surveyor. I think you're right though, if he really wants it he'll pay for the survey.
@Wayne Brooks - He has seen a copy of the county GIS map but I guess that wasn't enough for him. However, given certain context clues from our conversation, it's also likely that he isn't very internet savvy, so it may be more difficult for him to get full use out of the GIS map.