If he cleans it it probably will add a grand to the price...in seller's opinion.
Guys, the seller is asking a very fair price for a "mint" pair of JBL L300 (taking his word for it, as I have not seen them, and they look dirty, plus he uses them as shelves for his sh*t). Be advised that JBL L300 is considered one of the very best speakers of all time, currently, if you do a search, you will see them listed between $5,000.00 and $6,500.00, and outside the USA add about $1,000.00 to those prices. The pair being sold probably need some cosmetic TLC as the JBL logo seems to be in the wrong corner, unless they are upside down, as the logo goes on the bottom right corner, and obviously they need cleaning; though from the pic one can assume that they are dusty and could be easily cleaned.
So, if you have the money, I recommend you to go and see them to check their cosmetic and working condition. At $3,500.00, believe it or not, they are a bargain, and wouldn't be a problem cleaning them yourself. One of the most beautiful vintage enclosures you will find: Wood and Black Piano Finish.