Basically I have an old car. All estimates given were verbal. After everything, the total ended up being 6k of work. I can finance about 3, which leaves 3 for me to make cash. In the event that I cannot pay the bill, what will happen?

I assume my car will get repossessed by the mechanic and sold at auction, but how will this affect my credit? Will this affect my credit at all? Has anyone had a similar situation where they were able to settle on the final bill? Any insight is welcome and appreciated