Well you know what is wrong with the house, and you wont have to move.
Make sure that you do not pay too much for the house, perhaps have the seller agree that the price will be based on a professional appraisal.
Most likely the seller has looked on Trulia or somewhere to get an idea of the value. Trulia is based on properties that are on the market. Many of which are fixed up to sell. Your house will be as is.
You should probably ask the seller to pay all of your closing costs as it will be a lot less expensive and easier for the seller to have you buy it.
Properties with renters typically sell way under the market.
If you would like to get pre-approved for a loan give me a call, My pricing and service are extraordinary. I am also a licensed real estate broker and can walk you through the process at no extra charge.