Looking for Advise - Selling Car

37zeroZ

Me and the wife have decided to sell the Z. Had it exactly 8 years and feel it's best just to sell and use the money to add to the principle on our house. Our goal in the beginning of the year was to pay off the house by the end of the year and selling the Z would make this happen sooner. Anyways, looking for advise if the offers I received today from Carmax and another online buyer are reasonable. Carmax offered $15,000 and the online buyer offered $15,500. Pretty close considering they assessed the vehicle separately.

My vehicle is a PW 2010 Auto with Sport Package with 14.690 miles. The options I added at purchase was the illuminated kick plates and rear spoiler.
Always garaged, never smoked/eaten in, and no issues with the exterior or interior. Here's additional info and things I added over the years:

• New Continental Extreme Contact DW tires replaced at 13,356
• AAM Competition S-LINE Axleback Exhaust w/ S-Line Midpipe (Titanium Tips)
• Stillen Dual Hi-Flow Intake with Stillen GroundIing Kit (Red)
• Redline Battery replaced 6-months ago
• ZSpeed 370Z V2 Aluminum under Shroud Engine Splash Shield
• WeatherTech Front floor Liner
• PPF Clear Bra on Full Hood, Fenders, MIrrors, Bumper and Splash
• Trunk Tonneua Cover
• Satin 370Z Hood and Read Deck Emblem
• GT-R Start Button.

I don't expect to recoup the cost put into a vehicle, but it does help with the appeal when selling especially new tires and battery. What do you think of the offers?