There probably is some other site.
However, eBay is THE site for sellers looking for top dollar in a worldwide market.
I have bought/sold many musical instrumnts there over the years and cannot see myself buying/selling a musial instrumnet anywhere else.
I bought a Martin 12 string guitar there a few years back for just over $1000, plan to sell my $2500-3000 1930's Martin Ukulele there in the near future.