Well, it’s not quite that harsh — but you have to (1) have *some* clue, and (2) actually know what a reasonable completion budget is *before* you start.
Oh, and also not spend fricking $65,000 on installing some wainscoting, and matching trim.
So, I look at that budget and think: $335k, after deducting the trim extravagance, and then probably trim another $100k by acting as their own GC and eschewing the fancy. Which would’ve put them at $270k (+ hundreds of hours of unpaid work) in to a $300k house. Which is *still* a bad deal.