Yes, the question should be, 'How can my friend sell some of his lesser basses to raise cash for a superior bass?' This way you can pretend you're thinning the herd but you're actually still buying basses...
The way to tell you have too many is when you find each time you go and try one of the basses you've not played for a bit, you find they always seem to need a new set of strings and it feels like you changed the strings the last time you used it.
