I have a rehabbed property in a good neighborhood and I was trying out few things and was surprised to see the opendoor offer close to the market value. 

I am surprised as what you have accomplished should be the goal.  

If they do their due diligence and verify the numbers prior to purchase, what are the surprises that get them?

There are always surprises and new challenges to deal with, which is why I love it!

People will get creative with people who they believe in, but if it's just blind bids for a random customer that they don't know, then I'm surprised they aren't asking for 50% upfront.  

I did a little creeping on facebook and he is bragging about buying the vacant lot sight unseen and how surprised he was to find a foundation. 

Should be, but your language is a bit less than precise* so good to check on the details with a professional (*not at all unusual or surprising as most peopled don't do this every day).

You will be surprised, but there are some great opportunities out there, especially for foreign investors.

I would be surprised if anyone did.

And be sure to check with folks other than your family banker (where you carry all your accounts) - you'd be surprised how much price / term shopping can save you on your first few deals.Best of luck to you and I look forward to following your journey!