Are the 200 dinars that I took in exchange for maintaining the car and the effort of searching for it permissible, knowing that I bought it for 5,0 dinars and sold it for 5,200 dinars after maintaining it with my own money?

If your neighbor asks you to buy a car and you agree, this constitutes an agency (wakalah). If you purchase the car with your own money, you are to be reimbursed by your neighbor for its price. As for the maintenance cost, it is an unauthorized act (tassaruf fuduli). If your neighbor approves it, then it is valid; otherwise, it is not, because the agency was only for the purchase. The amount exceeding the price of the car and its maintenance is not your right unless you have agreed with your neighbor that it is your fee. You must inform your neighbor of the car's true price and what you spent on it, and then you both agree on a specific fee if you are not donating your effort.