clutch does not seem to catch fully when releasing it

This is a manual 1995 Civic LX, but I suspect the diagnosis would be the same for any manual car.

When releasing the clutch in 1st gear, it doesn't seem to catch cleanly. I hesitate to say "slipping', but the car starts off sluggishly even though I'm stepping on the gas to get it to go. There's no obvious problem in higher gears.

I searched for transmission and clutch problems but everything described on the web is so much worse than this one. There is no noise (well, maybe the slightest bit of grinding) and no other problem driving the car.

I am going to sell the car and don't want people to test-drive it and say it's not in good shape.

I would appreciate any suggestions.

You could try bleeding the clutch and see if that helps. When was the last time you replaced the clutch? When you did replace it, did you do the proper break in process or just drive it as-is?