Not a common problem. That could be from accident. As for price you can get a days membership for $4.95 to www.galves.com and print out the price sheet and have it with you to negotiate with seller. Galves price is usually trade-in price and therefore lower than private sale price.
I have not owned 4.6 so not aware of any specific issues. 2002 was first year of 4.6 so had some bugs but must be out by now that it has 77k. Pre-facelift had little more issues than after facelift.