I have seen this too many times.  IT firms come in and fix everything and then want to charge monthly for “maintenance”.  Most of the time when I am called in it’s because the IT firm who was charging for said maintenance isn’t fixing anything and in some cases are quite amateurish in their setup.  Frankly if you design it right the first time you won’t have to do “maintenance” in the way that is typically charged.  I have walked into networks too many times setup in such a way that once the previous vendor is removed it is nearly impossible to fully gain control of the network itself and totally lock the other vendor out.  Any subscriptions I recommend have the option to be totally controlled by the client with little or no direct involvement by me after the work is complete.  This starts with my Sophos UTM gear all the way to the desktops with AVG Cloudcare.  All of it can be managed by me OR not managed by me at all whichever the client chooses.  If the environment warrants it I will suggest me coming out in a few months or 6 months to check the machines for dust and dirt but most times it really isn’t necessary.  Service contracts usually are just an expensive way to make sure that something that should be properly designed works correctly.  I do not have a network that is so unstable that it requires constant attention.  if a network gets unstable that means there is a problem.  Problems need to be fixed not monitored.  I can install monitoring software and I usually do but since it costs me nothing I feel no need to charge the clients.  Certain alerts will generate a phone call from me to the client and then a repair if needed.  That one time expense is always cheaper than the ongoing and often unneeded expense of somebody babysitting a network that should be running correctly in the first place..:)