If your CPA doesn't have viable solutions for you, then make sure you exhaust your idea with more professionals as you may outgrow your CPA's "traditional" knowledge.

The house is listed for just under $600K, but it has significant damage due to broken pipes.

I can pre-authorize an amount and if the expense is below that, the vendor can do the repairs without talking to me live4) Urgent maintenance issues - say a pipe breaks, or tenant is locked out.

Is there a chance the water was on and all the pipes froze and then flooded the place?

You're going to want to follow the following general rule of thumb:- 0.5 mile radius- same zip code- Sold in last 3 months- Same unit count- Same bed/bath count- Same square footage(this is not fully exhaustive but they're the big ticket items)If the appraiser selects comps that are closer matches to the above than the comps you want to use, you're going to have a tough chance arguing for the usage of your comps over theirs. 

I can pre-authorize an amount and if the expense is below that, the vendor can do the repairs without talking to me live4) Urgent maintenance issues - say a pipe breaks, or tenant is locked out.

Will see how it's shapes up for due to some other constraints like angle of stairs coming down and movement of drain pipes.

May be a pipe dream though. 

Probably won't be any amazing deals, since he's not under pressure to sell, but might be worth a look if you exhaust what you can find yourself.

The property was unlivable at the time, broken water pipes, frozen boiler and water damage.