Nmf_69, IMO, I don't think a 2009 build date automatically means that the unit has seen a better day. The only moving part is the Phillips transport, which is supposed to be pretty hardy. Even if the transport goes, Kalvin recently told me that ARC has a robust supply of replacements.
As far as the electronics are concerned, ARC uses top grade parts. I think it's fair to surmise that 5 years of use is NOT significant.
But why guess?? Call Kal at ARC and have a discussion. I always found ARC to be tops when it comes to customer service. Kal might suggest that you take the CD-8 to a local ARC authorized service center/tech for a check-up.
Having said all that, I have a BIG concern. Your OP mentions that the HiFi shop that sold the CD-8 to you represented that the unit was 1 year old. I find that very curious, especially with a 2009 build date.
On the one hand, if the rep is true, does that permit the inference that the CD-8 sat around unused for the last 4 years?? Seems very unlikely, but if true, a quick start up could damage the unit if the caps dried out. Even if the CD-8 was used in the most recent year, what happened during the other 4 years??
On the other hand, and this is a "big hand," I place a very high premium on honesty and take very unkindly to dishonesty. The shop may have a perfectly plausible explanation, but if not, I would be inclined to take the unit back -- if the shop will refund your money.
Finally, I don't believe you mentioned how much you paid for the CD-8 or whether you are using ARC gear in the rest of your system. My rig is all ARC and IMO there is a wonderful synergy staying "all ARC." If the shop can credibly explain the apparent discrepancy and Kal can give you some comforting advice, you may want to keep the CD-8. I have the CD-8 and I think it's a great CDP. However, if the shop misrepresented age and use, that's a whole different can of worms.
Let us know how you make out.
Good luck.
Bruce