$12K is low for that car IMO and will sell in a heartbeat at that price.
I'd go for a bit higher $15K at least and wait for the right buyer. I get you are under no pressure to sell it.
Zero chance $12K is low. We've talked about this numerous times; your perception on what E90 328is are worth now is way off.
It's a 13-year old sedan now; Sailor keeps his cars in tip top shape but you can find them for under $8-10k all day long with more (average) mileage on them. I think $12-13 retail, $9-10 wholesale is the number.
For context, we just moved a PERFECT 2010 328i xDrive with the iDrive navi, leather, and 82,000km. Original owner, but on taking it in, it needed the oil filter housing gasket, valve cover gaskets and rear shocks. Sold the car for $10,995 certified and it moved. We bought it for about $6,500 from the client and did all of the work after the fact, put new fluids (brake fluid, oil) in it, and a new set of tires. Ultimately, the car's sorted and we made about $1,500 when all was said and done.