There is a phone number for the assumption department, but no one ever answers the phone or responds to voicemails.

thanks chuck, clay was one of my first phone calls.  

It would be best to ask your lender versus the uninvolved BP community.But, since you asked, 25% is a common requirement for banks' best rate for investor properties.  

Is it common for Real Estate Agents to overlook this?

If you can find a phone number that might be better, but the best thing to write in the letter is the truth. 

If you're looking looking to invest in larger commercial properties (multifamily, offices, industrial, etc) - personally or through a partnership/syndication - then you should be more concerned with the points raised by @Caleb Heimsoth.My article on choosing the right real estate market and avoiding the most common due diligence mistakes should help you get started. 

I found a few cash buyers through a software and looked them up on internet to find their phone numbers.My question is how do i introduce myself on the call?

Sloping and mortar cracks as well as noticeable settling are all common.

It is common to have a lager down payment that is not refundable in a "lease option" deal. 

hot markets thats common.. not sure what your wanting or expecting.