The credit and down payment requirements may be slightly higher, but nothing unreasonable.

I don't think that's unreasonable.

I, on the other hand, do not have a track record of success, and so it is almost unreasonable to try to find investors willing to commit to the possibility of me ever bringing them a deal, and then not really knowing how well I will perform.A very solid option for you might be to get pre-approved for as large a mortgage as possible, so you know your own price range.  

The turnkey providers need you to believe that 50% is unreasonable, because their deals fall flat if you stick to it, they need you to estimate 20% expenses.

As far as ten days, that is not unreasonable and much better than  the unlicensed FRAUDS AND SCAMMERS asking for 30 or 60 day "inspection period" while they are trying to find a legitimate buyer. 

A lot of the potential sellers I meet with lately are very unreasonable about their asking price vs the reality of the condition of the property.  

That area rents $1050-1500 with amazing finishes, so $600-650 for that property aren't unreasonable.

This sounds like a legal disaster waiting to happen when the bank rejects the short sale or counters with an unreasonable price.

An unreasonable seller is another. 

And is it unreasonable for me to buy on what I believe I can get the NOI to pretty quickly?