Administrative or servicing errors
As much money is lost to these errors as is lost to dumb buys. Each state has a set procedure of things you have to do to protect your interest in the property. THESE ARE NOT OPTIONAL!!
We always suggest you get a good lawyer who understands the tax sale laws, because if you make one 
mistake (in Indiana you have to “notice” every interested party). This noticing has to be done in a specified window of time – if you are a day early or a day late you stand a good chance of losing 100% of your investment.
I went to law school – never practiced law and felt I could read the statues and understand them but I always hired a lawyer. Read the statute, get an attorney to explain that which you don’t understand, and follow it exactly. The taxing authority is not your friend here. They are delighted you bought the lien, but they would be just as happy if you screw up and their resident (who lives there and votes) does not lose their property. The courts are reluctant to take away the property owner’s property and will take any valid reason to deny your application for deed.
Learn what to do about subsequent taxes. In some states if you don’t buy the subsequent taxes; a new lien will be sold and that lien can take away your lien. Learn the life of your lien, in almost every state the lien expires as worthless if you have not applied for deed or foreclosure within a statutory period of time. Find out if you can contact the property owner. In some states you can, in Florida you are prohibited from doing so.
Doing so could cost you your lien.
Find out if you have to record your lien or certificate. If you do, do it- if you don’t you will lose 100% of your investment.
Don’t make payment plans with the property owner unless your attorney tells you that it is permissible under the state law. In a number of states you lose the security of the real estate lien if you do so.
If you happen to discover that you have, through error, bought a piece of property that has an EPA contamination notice – do not go to deed under any circumstances unless you are qualified to evaluate the clean-up cost. YOU WILL BE LIABLE TO CLEAN IT UP IF YOU GO TO DEED.
Do not enter into bid rigging schemes. Any agreement between bidders as to how they will split up the parcels or what they will bid is illegal and your purchase can be made invalid, plus you can be prosecuted criminally. You will meet people at every auction who want you to enter into such scheme. Listen to what they say if you want, but never participate.
If you listen to what they say you will know what they are doing and can plan accordingly, but do not enter in to any agreement on bid rigging. There have been a number of cases in the past five years on this issue.
Don’t let all this scare you away. There is a fairly simple solution. You have the attorney make up a checklist, in calendar form, of when you have to do what and make sure you do it. Even better, hire the attorney to do the work for you, the money is well spent and he has malpractice insurance if he screws up.