Everything was good till paperwork time didn't not...

Everything was good till paperwork time didn't not buy since not willing to budge on price on the 2010 dodge journey with decent amount of rust on back side. Vehicle price 1000+ over kbb value not willing to negotiate on price then when looking at paperwork I found that the intrest rate was raised 3.77% without telling me. When I confronted guy he said ohh I thought it would be xx% rate but it's actually 3.77% higher then what I last said. Guy didn't say anything until I said something about it. Felt like they were just trying to take advantage of a young family. This is just my experience buyer beware make sure you look at every single line and documentation to make sure nothing changed. They lost a customer due to not negotiating on price and not telling me the interest rate was higher then what I was last told