NEVER RELY ON THE SELLER'S ASSURANCES IN A USED CAR SALE IF THERE IS AN "AS IS" STICKER IN THE WINDOW!
If there is an "As Is" sticker in the window, you should treat the salesperson as if they were wearing a sign that says "You cannot rely on a word that I say." You MUST take the car to your own trusted mechanic and have that mechanic do a thorough inspection, including a compression and timing check for all cylinders, checking for signs of undisclosed frame damage, suspiciously new components, etc.
If you cannot afford this pre-purchase check, you can't afford the car anyway, so get away from there before you get ripped off.
REMEMBER: There are no used cars being sold in Oregon that are too good to pass up. There are plenty of good used cars being sold every day for a fair price -- if you miss one, there will be plenty of others available when you've saved up a little more money.
By the way, like many people, the caller thought that there was a 3-day right to return the car. Nope. If you sign on the line and drive away, you. are. stuck. So be sure before you do!
P.S. Never finance with the dealer. Arrange your financing before you shop with your credit union. (You are in a credit union, right?) Don't discuss financing at all until you have picked the car you like and your mechanic has done a thorough inspection. IF, at that point, you still want the car, negotiate with the dealer without disclosing that you already have financing. If the dealer quotes a price, ask if that is the best price and ask what the cash price is -- since you have your own financing arranged, you are the same as a cash buyer, which merits a discount.