I have purchased tax properties in Alabama. The biggest thing you need to look for is that redemption affidavit. On my first house, the taxpayer sent me the blank affidavit and nothing else. I had no idea what it was she did not even include a letter requesting the preservation costs just that blank affidavit. She then faked a letter in court, lied and said she sent it with the affidavit. If you don't reply to that redemption affidavit within ten days you lose all rights to your preservation costs by the same token if the homeowner does not reply to your preservation costs with a specific action within 10 days they lose the right to dispute your preservation costs. (or they should according to the law but you will quickly find out that what is written in the law does not matter in Alabama unless you can fight it out in court like all the way to the State Supreme Court fight)
A good idea is to communicate with the redemption office and make sure you file any amounts you feel you are owed with them as well as copies of the communication and proof the taxpayer received the information such as a registered mail receipt. (unfortunately, sometimes this might not be enough but it is better than nothing)
Another thing you have to watch out for is taxpayers lying and telling the redemption office you have not responded to their request to redeem. They will then be allowed to redeem behind your back, without paying you for insurance or preservation costs. The redemption office knowing you and having information from you such as copies of your response to the affidavit and proof of reciept can help avoid this.
Alabama is hard to buy in, even the judges will admit they don't fully understand the law because it is ambiguous. I probably would not buy here if I didn't live here because they do make everything incredibly difficult and the people at the courthouse give the worst advice and opinions (even when you don't ask). Be prepared to take everything to the courthouse in person. They will freak out if you ask to mail in paperwork and ask a million questions as to why you can't stop your day to drive down to the courthouse to hand them a document that could easily be mailed, e-mailed, or faxed. You can easily lose your investment missing a deadline or because of the judge not being satisfied with your notification to the taxpayer (had this happen too. I use software for my invoicing judge completely ignored the invoice and allowed a taxpayer to redeem as if I had never responded. It was incredibly frustrating because the law does not specify how invoices have to be sent she basically just added her own rules after the fact that investors somehow should magically know through osmosis I guess.) With that being said if you are not a lawyer I suggest you find one that can help you file suit in the very likely chance that taxpayers are allowed to redeem without going through the process properly. It happens a lot you will need the attorney to file the revocation petition when this does happen. Scrambling to find an attorney after the false redemption is a frustrating and expensive task. If I am not mistaken the only legal fees you can charge are for ejectment costs so you definitely don't want to play the redemption revocation petition game, those legal fees (Think $500 an hour in Attorney fees alone) could easily kill any profit you did have and if you lose you could end up losing your entire investment and then some.