I was not trying to insult you, but you are in denial over the true condition of your car which is dangerous. The rust damage in your picture is very major, and damage that bad is rairly localized in a single spot. This is what a healthy frame looks like.
Comparing this to your picture, at least a 1/3 of your frame on the driver side is toast and is ready to snap in two at any time. At the least you are looking at a chassis swap. If the seller told you the truth, the car may have been sitting directly on the ground at some point which would cause such extensive rust. Though to me it looks like it rotted from the inside out from salt sitting inside the rail, POs often lie though their teeth. I have not even seen rust that bad on junkyard G bodies, and with damage that bad most if not all your body mounts are going to be rotted too. Did you do a hammer test on the rest of your frame?