I'm a little surprised the conversation has gotten this far with little to no direct talk of opportunity cost (OC).
I don't believe in "overpriced" / "underpriced" as a concept unless you are talking about commodities. Real estate is NOT a commodity: every location is different, even within a building itself. The pent house commands more rent than the basement, usually. We only know if someone "paid too much" (if ever) years after the fact. And I'm not sure we know even then.
Rather, I think we do well to talk about OC: "I only have enough money to buy apartment X for $Y, or I can buy investment Z for $Y. Which one will I take?" Then if that choice accomplishes the investor's goals, the term "overpaid" becomes irrelevant.
Could I have bought it cheaper? Possibly. But that is true of almost anything. Let's pretend Bob owns a 100 unit apartment complex and he has it listed for $10 million. If I buy it today and it cash flows positive, did I overpay? What if I had waited 10 months and meanwhile he has a life emergency, needs cash quick, and he would have dropped the price to $9 million? Did I overpay at $10 M? Nah, that's silly to look at it thru the lens of the future and the "what if?"
That's why I believe opportunity cost is the key factor to look at. I have $X to invest and this range of choices. Which one do I believe will best help me reach my goal, whether that's cash flow, appreciation of the asset, parking cash for safekeeping, enjoyment of the utility the asset brings, etc.
I know a person who paid $1,000 for a bottle of bourbon. Did he overpay? As compared to what? What if he makes $1M income per year? $10M income per year?
Me? My bourbon costs $45 or less.
Set your goals, go forth, and conquer!