I have many years of experience repairing poorly hung doors, cockeyed jambs, sticky locks, etc.  

Whether it's an exterior door or an interior one, Masonite, fiberglass or hardboard, elegant exotic wood or doug fir, if the door is worth saving, I can almost always repair the installation. Door hanging is a skill which takes years to master, and the woods are full of "door hangers" still learning the trade.

Mortise locks, in particular, are a specialty of mine. Mortise locks, while  beautiful and extremely functional, can also be a problem for the home handyman. They are among the strongest locks available for a residential door. They do, however require expert installation and maintenance because of the multiple assemblies comprising the lock. A poorly installed lock is usually a source of frustration for the homeowner, and mortise locks doubly so. However, many repairs to mortise locks are quickly effected, and relatively inexpensive. Baldwin, for example, provides an excellent warranty, so that many parts requiring service will be supplied by the manufacturer at no charge.