It involves a legal battle, a fraudulent contractor and much more.  

A transaction lending company I am involved with will send proof of funds letters

In the end, this means you are not actually "spending " you money...you are "using" your money, as many times as you want/can.Second, the success of this strategy as @Brent Coombs has touched on, is very much Market based (as in dependant on the RE Market you are investing in) since it involves getting properties at a discount.Third, it works best when you are using all cash, or a cash-like substance.  

I've also heard some larger property management companies will offer that service, though I'm not involved in that side of real estate enough to have seen it myself.

i'm not sure if I'm the best for advice but I'll gladly give you me few cents due to my experience.I have been involved with real estate for 3 years probable more but took action this year specifically May of this year.

I have been involved in the property management field for a few years now but currently do not own any rentals of my own, me and my business partner currently concentrate our efforts on flips.

No broker involved.  

I see improvements as being more minor work, perhaps requiring less skill (e.g, cosmetic improvements like carpet and paint) and rehab as being a project being truly rehabilitated and much more involved.  

The last time I was involved in a transaction like that, I was buying a car and could almost literally feel the salesperson's eyes sizing me up to determine what he could squeeze out of me.

There are so many different expectations, so I think it's best to ask what they are looking for, and find a solution that works best for all parties involved.