Our tax records/deed transfers are not online in Suffolk County yet. If you are curious what homes are selling for, I can set you up on an ongoing free report which will let you know as things come up in your area of interest. Just email me privately, firstname.lastname@example.org.
If your next question is how can a home buyer get access to all that the answer is to work with a Realtor. Perhaps the best way to explain why you need to do that is to say that if you decide to bake some bread, you needs not only some flour, but also some yeast, then you need the two to work together to rise before baking. Without the yeast, you are going to end up with a very flat loaf of bread, and even if you can get the yeast through a friend of a friend, you still need to bake it, or it will be indigestible. It's not accessing the data that's the most critical (although obviously key to the analysis you are trying to accomplish), it's how you interpret the data that is the real skill and is what sets apart one agent from another. If you would like information on a particular area, you can contact me offline at email@example.com and I'll see what I can do.