I cleaned mine ok with lots of tedious caution and a little flash light, but am hesitant to recommend it as a DIY service to others since it was harder than I imagined and since I believe many AC companies will come do an annual service with coil cleaning for around $150 (again, just guesstimate) and likely have a method more foolproof than my aerosol cleaner can and garden hose, plus they can look the system over and catch/fix any small issues before a home inspector would find them. 

I believe a great strategy for Tenant Screening, other than the usual Background/Credit/Income checks, is to get a letter of recommendation from the current Landlord AND, at the same time, PROVE that they have paid their rent for the last 12 months ON TIME and are CURRENT on their rent.While no strategy is foolproof, this one prevents getting a letter of recommendation from a Landlord who just wants to get rid of a bad tenant.Bad tenants probably 95% of the time are not current on their rents and certainly do not have 12 months of on time payments.While I didn't implement this until recently, one of my tenants that is searching for a cheaper apartment was asked to give proof of on time monthly rent payments while I gave him a Letter or Recommendation.In other words, the on time monthly rent payments corroborated the story given by the Letter or Recommendation.While I haven't had a tenant issue for the last decade, I do believe this is a GREAT strategy to try and weed out bad tenants.From now on, this has become my policy.I also let some of my tenants who have a habit of paying late that their Rent History is very important and they should treat it more important than their Credit History.If you can prove you have a great Rent Payment History, dings in your credit which may have come from something like a Divorce, etc. can be looked at in a better light, or so I believe.All my tenants are on an online Payment System, Rentalutions.They all have access to their Payment History and can produce a report.

Just saying, don't think of them as a foolproof way of preventing theft.

We have a few good ones here and while it's not foolproof, they do a decent job and you only pay if they collect (they keep a portion).

However, before that, we relied solely on Rent Screening, which provided an exceptional service with no issues to report.It's noteworthy to mention that there are several new entrants in the market claiming to offer foolproof tenant screening, simpler income verification, document validation, and bank verification - FinDigs being one of them.

Don't get me wrong; there are plenty of issues/problems/quirks that old houses have that new houses don't, and an old house can obviously have hidden problems and big repair/maintenance bills too--which is why thorough due diligence is fundamental to REI...but, the point is: a brand new house is not a foolproof solution to repairs/maintenance headaches (and in some cases, a brand new house can be a much bigger gamble than an older house).This is a particularly important lesson for inexperienced investors, who tend to be the most prone to "shiny object syndrome" (the tendency to let nice aesthetics distract from real, underlying issues).

Originally posted by @Kevin Sobilo:@Frank Chin, many problems don't have one simple foolproof solution, but if you label cans with black paint or marker, it should remain readable.