Samuel, here is how we do it in our business. We pull all of the sold COMPS over the last 3 months. Even though we are not realtors, we can do this in our area because the Property Appraiser here is online and shows all properties sold.
Next, we go to Zillow and Cyber homes. We NEVER use these sites to determine the value of the property, but they are good places to identify additional COMPs. We have found that in our area Cyberhomes is usually fairly accurate, but you can not take that as gospel, since they do not necessarily use like COMPs all the time in their formula.
Once we have all of the COMPs in a 1 mile radius over the last 3 months, we average them, subtract what we feel repairs will cost, then multiply that by 70%. From this number, we subtract the profit we want to make from this deal and that will be the top amount we will offer for the property.
Let's take an example. You have a home that is worth $120,000 ARV. There is $25,000 needed in repairs (contractors estimate). You want to make $8,000 on the property. Now, we have all of the numbers we need to identify our highest offer, so that number would look like:
(($120,000-$25,000)*0.7)-$8,000=$58,500
That means our highest offer will be $58,500. Remember that the FMV is currently only $95,000 ($120,000-$25,000).
Now, we have come across properties that look extremely filthy and awful inside, but would not require a tremendous amount to fix up. We currently have one just like this. Our first offer on this property is $34,283. We never use numbers that can be evenly divided by 10 (i.e. $38,000). By using a non-conventional number, it appears to the lender that we have done due diligence and believe that is the true market value.
All of this is the easy part. The more challenging part is influencing the BPO/appraisal. That is where you make your money. The lower you can get that BPO to come in, the easier it is for you to purchase the property at a price that will allow you to make a profit.
Remember, the COMPs you use should be comparable to the property you are looking to purchase (i.e. +-10 years, +-200 sq ft, comparable bed/bath, in the last 3 months, less than a mile from the property being purchased).