I have also always managed our IPs. We've only ever had three at any one time, but now I also manage a few that our parents left to us.
I bought my first IP before I was 20, so now at 54, I've been doing this for well over 30 years. In all that time, I have only had issues with one tenant leaving rubbish and damaging the house, and my mother had two issues with bad tenants. One went to tribunal. Mum represented herself and I went for support. Tenants made jackasses of themselves and got $12 of their bond back
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For many years we sourced tenants from the newspaper. That was the only way until the internet came along. Then we used the sites we could get on before re.com was able to be sourced via different paid sites.
We have used agents, both successfully and not so successfully. In all that time we have never done a check and have used gut instinct, which has rarely let us down. Perhaps part of that is that our IPs are in better areas and the risk of having feral tenants applying is a little lower...?
I cannot begin to count the thousands we have saved over those years but I think the difference is that I learned "at the knee" how to manage tenants, how to paint, renovate and maintain houses. My parents are gone now, but I owe them both a lot for the valuable lessons learned.