An appraiser generally works only from comps - which can be tricky in a rising market because even if the house three doors down sold for $1m two months ago, yours may now be worth $1.2 on the open market - but with no comps to justify it, the appraiser can't say that. And when you buy it, you can only base your ARV on the comps. That's what the buyer's bank will base the mortgage on - not $1.2. Which doesn't necessarily mean you don't list it for $1.2 but you need to be able to make money on the ARV of $1m. (even the lowest priced houses here are more than $1m)
And I think it might be a conflict of interest or something for an appraiser to work with an investor. I'm not sure about that but it sounds a little nefarious.
The thing is, a good agent, but more importantly, a good investor must absolutely be able to calculate their own ARV or you will be ripped off. Simple as that.
But not that simple.
But luckily I can suggest a few things - some of which I learned from J. Scott and D. Manolo above, two of some of the most well-respected contributors on this website (but I didn't put the @ because it would be a bit embarrassing for them to say that). Anyways, 1. buy the books 'The book on flipping houses' and 'The book on estimating costs..' both actually written by J. Scott and available for purchase on this website. 2. then watch the webinairs or read what's written by Brandon Turner - he'll explain how you absolutely need to know the ARV, the rehab estimate, and the minimum amount of profit that you want to make on a rehab - before you even consider making an offer - because THAT is the only way you can arrive at the offer price.
And you need to hit the streets (the open houses would probably be OK too. Lol) and start determining the level of improvement in neighborhoods. If you under or over improve for the neighborhood, you will always lose money - which is probably what the flipper in your example did.
Best of luck!