TromboneChat

I was just browsing Facebook marketplace and found a listing for a (seemingly) silver/silver-plated King trombone listed around $500 under "King Trombone". There aren't any closeup pictures of the bell/engravings so I reached out and asked if they know what model it is and if they can send me a picture of the bell markings to see and they said they're not home but that it is a 606.
I can't really find any good information or comparisons of the 606 to 606SP, even the Conn-Selmer website doesn't have a picture up of the SP model. I imagine these aren't super common horns, but does anyone know what they could be valued at or if it would even be worth entertaining trying to haggle the price? I don't think many used 606's would be worth $500+shipping for me personally.

I'm not sending any considerations their way until they send some more clear photos, since I know that certain lighting can make normal lacquer look silver-ish but I'm pretty sure this is really silver-plated.

Yeha for a silver plated 606 that's not unreasonable if its in good shape.

The King 606 and 606SP are student level horns.
The 606SP (silver plated) horn is rare, but is not a desired collector horn commanding a premium price.
Silver plating in pristine condition will not add significantly to the value, and damaged silver plating is a big turn-off.
Unlike lacquer, damaged silver plate cannot be easily repaired.
Ebay is a good place to get a feel for prices.
Search for King 606 and you will find many offered.
At the left of the screen, scroll down to the box labeled "Sold Items." That gives the final sale price, as opposed to the asking price.
Caveat Emptor !!!!!
Buying a used trombone from a stranger Online is a huge risk.