Assumable loans just don't exist anymore and are usually not in anyone's best interest. The seller losed their equity, and can be held accountable for a loan default, the buyer can get a better interest rate these days, and the bank assumes too much risk so they don't usually agree to it.
Some investors offer Wrap around loans and are doable if you (1) go through an attorney and (2) work in cooperation with the bank. Some investors get into this type of bail out in order to help distressed homeowners. Their objective is to release the owner from making the morgage payment and the new owner continues to market the house to a new home owner hoping to sell it at a profit. The investor tries to work out a negotiated rate with the bank. However, if you ask me, the whole thing is a scam and many realtors won't even deal with it, it's part of the aftermath of giving loans to unqualified buyers (subprime market).
Your comment didn't note if it the purchase is for you or for an investment. If it is for yourself then you really need to look into getting your own loan and start fresh. It also seems to me that with today's low market rates that you could find a good loan product. If you are having trouble getting qualified then that is a whole other issue. If you would like to visit with me about finding a good home/good deal and need help with financing I can certainly help you.
RE/MAX Alamo Realty