Widow Needs Advice--Marantz AV 7005

Hi All,
I’m a widow at the tail end of selling my husband’s estate & I’m hoping this post is okay since it discusses pricing.(I’ve posted a few times before seeking advice and I was so grateful because everyone was overwhelmingly helpful. This is a great community!!)

Here’s my dilemma:
I listed his Marantz AV 7005 for $425 in mid-May on FB (local pick up) & today I got an offer for $350. (I used hifishark dot com to determine my pricing & priced it towards the low end.)

I haven’t responded to the potential buyer yet because I wanted to check hifishark dot com again to see if selling prices have changed. (They haven’t.)

The Marantz is in excellent condition (hubby babied his electronics) & it works. (He was using it up to the end.) I’ve got the original packaging & box, the User Guide, Remote, Power Cord and the Audyssey Omnidirectional Calibration Microphone. I also took good photos of the front & back--including a photo of it turned on--and photos of everything that comes with it.

Back to today’s offer. I thought to counter him at $400 (do you think I should?), but if he wants to stick to $350 I’m not sure what to do. Is this an item that will go down in value the longer I hang onto it? Thoughts??
EDITED TO ADD: Average selling price for this unit (in comparable shape) since January of this yera is $406. Just an FYI.