There are all sorts of "services" that such a necromancer could provide. It depends really entirely on what they can do, and if they can bind ghosts to do their will, there is really quite a lot that can be done.

1. Summon ghost to pass information to and from the underworld. Maybe a murder took place, and they need to find out who it was. Find a necromancer! Only uncle Joe knew where the treasure was buried? Find a necromancer! Sentimental wife just wants to talk to her husband who has passed away? Find a necromancer! This alone would be enough to keep a necromancer well-fed.
2. Spying. Yes, seriously. It may not seem mystic and in fact, it may seem downright absurd, but why not? Ask a ghost to eavesdrop in a nearby castle.. find out how many soldiers they have, with what frequency they change shifts, do they get drunk often? Etc. Want to find out if your lover is cheating on you? Get a ghost to tag him.
3. Can ghosts haunt objects/places? If so, you can be hired to send a ghost to haunt these objects/places. It would be an excellent way to keep people away from something you possess.
4. Create plagues. It would be an excellent weapon against an enemy castle. Hurl a couple vials containing these plagues and wipe out the castle without ever having set foot inside. Needless to say, if such a thing were possible, there would be a lot of plagues about, so presumably if a necromancer creates them, a necromancer can also create cures fairly easily, so this doubles as an antidote to plague manufacturer.
5. Expertise. Is the woman a witch or not? Necromancers would be considered the experts on this subject (despite being albeit a bit hypocritical to allow a necromancer but disallow a witch). A necromancer may honestly not even know how to tell, but this doesn't mean the people think that way, meaning a necromancer can still exploit these services in exchange for money.
6. Raise armies. No, they don't have access to corpses, but this doesn't mean that someone of power wouldn't try to befriend a necromancer in order to expand his armies. Usually laws are meant to keep the people in order, but kings and queens are above that order, so long as such things are kept somewhat discrete from the general public, and you had better believe that if a king or queen had a way of doubling his or her armies that he or she would do so. In that regard, having a necromancer, even one that has access to corpses, could be very useful, so long as his practices are kept from prying eyes and the general public.

Hope that answers your question.

There are all sorts of "services" that such a necromancer could provide. It depends really entirely on what they can do, and if they can bind ghosts to do their will, there is really quite a lot that can be done.

1. Summon ghost to pass information to and from the underworld. Maybe a murder took place, and they need to find out who it was. Find a necromancer! Only uncle Joe knew where the treasure was buried? Find a necromancer! Sentimental wife just wants to talk to her husband who has passed away? Find a necromancer! This alone would be enough to keep a necromancer well-fed.
2. Spying. Yes, seriously. It may not seem mystic and in fact, it may seem downright absurd, but why not? Ask a ghost to eavesdrop in a nearby castle.. find out how many soldiers they have, with what frequency they change shifts, do they get drunk often? Etc. Want to find out if your lover is cheating on you? Get a ghost to tag him.
3. Can ghosts haunt objects/places? If so, you can be hired to send a ghost to haunt these objects/places. It would be an excellent way to keep people away from something you possess. Similarly, a necromancer could presumably dispell the haunting of an object/place, which would be an equally valuable skill to have.
4. Create plagues. It would be an excellent weapon against an enemy castle. Hurl a couple vials containing these plagues and wipe out the castle without ever having set foot inside. Needless to say, if such a thing were possible, there would be a lot of plagues about, so presumably if a necromancer creates them, a necromancer can also create cures fairly easily, so this doubles as an antidote to plague manufacturer.
5. Expertise. Is the woman a witch or not? Necromancers would be considered the experts on this subject (despite being albeit a bit hypocritical to allow a necromancer but disallow a witch). A necromancer may honestly not even know how to tell, but this doesn't mean the people think that way, meaning a necromancer can still exploit these services in exchange for money.
6. Raise armies. No, they don't have access to corpses, but this doesn't mean that someone of power wouldn't try to befriend a necromancer in order to expand his armies. Usually laws are meant to keep the people in order, but kings and queens are above that order, so long as such things are kept somewhat discrete from the general public, and you had better believe that if a king or queen had a way of doubling his or her armies that he or she would do so. In that regard, having a necromancer, even one that has access to corpses, could be very useful, so long as his practices are kept from prying eyes and the general public.

Hope that answers your question.