I haven't purchased my first property yet, but I was well on my way a few months ago until the deal fell through. I'm certainly still looking but have changed strategy a bit.
My problem/mistake/confusion comes is related to finding or noticing problems in houses. The duplex I was going to purchase seemed good on the walk through the first time, took my wife the second time and nothing major was seen (some cosmetic stuff, old appliances and other things that I would be willing to fix). Then comes the $600+ inspection that found a huge list of things from missing spacers in the metal roof to lint in basement spaces that are fire hazards. Some problems, like the lint, are easy fixes. The roof problem is not something I would have realized, especially since the owner had just had the roof replaced. Yes, this was a brand new roof put on by the Amish folks that was not done correctly. I always thought their work was amazing, especially looking at the barns and houses they build as I drive through the Finger Lakes. There's a similar disappointing story (which I won't get into now) with my dad's metal roof that was done very quickly but poorly and not noticed until mold was found between roof and ceiling.
I know the issues that were found are rookie things that most seasoned investors would notice upon a walk through. The owner/seller was also the broker and he painted a perfect picuture of the property that glossed over things that my rookie eyes missed. Aside from taking a contractor through every walk through, I'm not sure how to find the detailed problems that the inspector found that cost me a good chunk of change.
Another mistake that I made in this deal was not taking my agent through the property becuase she was unavailable. I know this was a huge mistake becuase she would seemingly have seen some of the issues. I found her on BP but she lives an hour away. There are no BP investor/agents in my area which is disappointing, but I think knowing the area and having someone close by would be extrememly helpful. My agent was awesome and more than willing to walk through several other houses with me prior to this, but in the interest of getting this one done in a timely manner may have been at an expense.
On the positive side, a $600+ lesson is much better than a multi thousand dollar lesson if I purchased the house wihout an inspection to find out I had to put way more into it than expected. And I did learn a lot. The inspector was great, an enthusiastic teacher, and his report was detailed and full of photos.
All in all, in the future I would like to do BRRRR deals but while I'm in graduate school I'd like to purchase something that needs less work/ no work. So when it comes to the BRRRR strategy, knowing what needs rehabing, and then on top of that know the cost of rehabing will be quite the challenge. For me at this point, knowing when a property looks good enough (after the numbers work out using the rental property calculator) to put an offer in and pay an inspector is a challenge. I guess that will come with experience and more walk throughs with experienced investor/agents.