Trading in a car does not affect your credit unless you sign a new car loan and get a new car. This may negatively or positively effect your credit.
is there a tax credit when trading in your used car when purchasing a new one
No.
A Lot.
It has the same effect on the credit.
In general, you cannot return a car to a dealer. You can sell it back to them, though. Selling it won't affect your credit.
Your credit can raise or lower your credit score. It is what consumer credit for buying a house or car is based on.
Any default on any loan will damage your credit in the future.
Stays on your credit rating for 7 years. Has a very negative effect.
dude wheres my car
Bad credit will affect your APR on any new loan. Most banks use a tiered credit system to determine APR.
Only if the dealer reports it to the credit bureaus.