If I were looking to buy a used car that I noticed had one tire going flat, I would prefer to either get it fixed or fix it myself, rather than the seller just filling it full of "Slime" to get it sold.
The steering head and neck bearings are different terms for the same thing. To adjust the head pressure on the bearings is not a big deal. It should not be to expensive for a dealer or indy to adjust, probably an hour labor. If you are well equipped with tools and a jack, its something you can do yourself.
Basically, you have an adjustment nut which determines how much pressure is on the two bearings. The upper tree seats on top of this adjustment nut. Then there is a steering head nut which is torqued and keeps it all together. A "Fall-Away" test is performed to achieve proper adjustment.
If the bearings need replacement, its more involved because of the removal and replacement of the bearing races. This is probably not something the average owner has the tools to perform.