In case any non-pros want to touch up unisons on their own, like I have, I wanted to post my own experience here. I bought an inexpensive, but not bottom-of-the-barrel, tuning lever and had to return it because, believe it or not, it didn't fit my piano's pins!!
It was a #2 gooseneck lever (the one with a wooden handle that is available in quite a few places, including pianoworld, where I bought it). It fit only the bass pins snugly, and with the rest of the pins it was either just barely tight enough on the pin or not quite tight enough. I actually damaged a pin by using the lever.
Anyway, I recommend getting a quality hammer from the start. I now purchased an extension lever with a vinyl handle, and even though it too has a #2 star tip it fits all the pins on my piano! There is slight wiggle room on the tenor and treble, but it is almost completely snug and I can feel that no damage is being done.
I had a professional do a tuning a few days ago and one unison went out a little bit the next day and I think he didn't do some others as nicely as he could have (he only began tuning in 2006 and gave the lowest rate in the area). I have successfully used my new, more expensive lever to bring them all back to where I am happy with the sound.
The thing to be careful with, if anyone does this on their own like me, is to be conservative with how many unisons you work on, and how many strings per unison. The interrelations between the frequencies are such that if you do too much fiddling you'll have to get a pro back to fix it.
I should also add that I've done some reading in the Reblitz book and I tried to tune a spinet for about a week a few years back, so I have some experience, even if it's just experience about what *not* to do.
I'm sure the inexpensive gooseneck lever works on lots of pianos. Mine is an old piano, so it might be that the pins are slightly small. I did think it was worth passing on my experience here though, since I'm amazed that two levers that are both supposed to have the same head can be so different.
I'm also not at all unsatisfied with PianoWorld for carrying the inexpensive hammer. I'm sure it works out for lots of people.
Semi-pro; pianist and piano technician
Tracks on Spotify and iTunes: Daniel Pollmann Charles Lang 'Desert Music'.