There are other things to consider that may not be reflected in the records, such as improvements made, upgrades, etc, that may have considerably brought up the value of the home.
I love using the tax records to attempt to get inside the seller's head, as it can provide some invaluable insight, but ultimately, your offer must be combined with true, current comps.
What might be relevant in the research you are doing is finding out information so that you can make an unrealistic low offer. If one person paid $100k 10 years ago and their neighbor paid $500k last year for a similar home, you wouldn't make a $300k offer to the person that paid $500k but you might to the person that paid $100k. But you need to look at the comps to see if both homes are currently worth $300k. But your tax and history research is time wasted if the $500k person is trying to sell his home for the current market value of $400 and you are willing to pay $400k.
I would strongly advise finding a local Realtor to help you research comps, discuss market conditions and negotiate a strong offer.
private real estate investor, not a real estate agent
Again, I would caution making my offer based on what I perceive to be the previous owner's profit.