Don't sell it to your brother-in-law.
Read the above, then if you go ahead and do it anyway, when the first problem rears its head (as it inevitably will someday) or the second problem or the third and it sours your relationship, then think back and say to yourself, "Wow, BlueSky is wise."
I've been fortunate. My daughter bought my previous vehicle and though it has been a disaster, she is a mature young lady and it has not affected our relationship at all.
How bad is that car? If I hit the Lotto one day, I will first buy her a new car then take a pickax, sledgehammer, and flamethrower to that pathetic POS that Dodge built and called the 2000 Intrepid.
Unless you're VERY confident about the strength of your relationship with your B-I-L, do NOT sell him your truck.
ETA: As to your question (
) the best answers are 1) Let your bro-in-law take it to his own choice of shops as recommended by a previous poster or 2) take it to an independent you trust. Most dealerships will hose you from every direction if you give 'em a chance.