So....if you can only play one at a time, why do you own more than one?
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For me: I had a cheap beginner 4-string with PJ pickups. (1 bass)
I thought I wanted to start playing a 5-string, so I bought an (otherwise identical) 5-string. (2 basses)
Then I thought "hey--I like humbucker pickups better". So I bought 4-string HH. (3)
Then I thought "hey--I should get a 5-string HH." (4)
Then my bass teacher died (TB's own Michael Stanley. RIP.), and gave me one of his. (5 basses)
Then I learned that my favorite band, Type O Negative, tuned their instruments to B-standard. So I bought a 4-string tuned to BEAD. (6 basses)
Then I learned that not all songs are in standard tuning, so I bought another 4-string HH that I could use in alternative tunings, like C# standard. (7 basses)
Then I found a 1980 model Aria Pro II on Reverb. Since I'm a 1980 model, I just thought I'd go ahead and buy it. No real reason why. (8 basses)
An Esh Stinger I (the "Peter Steele" bass) popped up on Reverb, and since I'm a huge TON fan, I snagged it. (9 basses)
I liked the Esh so much that I bought another one. This one is EADG tuning. (The other one is in BEAD tuning.) (10 basses)
I bought a 5-sting fanned-fret bass, but don't like it. It's about to get traded in for a 5-string version of the Esh Stinger 1. (11 basses)
I bought a cheap "travel bass" from a friend. It's a piece of junk, so I don't really mind if it gets dinged a little bit. (12 basses)
I bought a jazz bass, because every "real bassist" needs a jazz bass. Now it's got flats on it. (13 basses)
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So that's it. 13 basses. I think I'm in "one in, one out" territory now.
Why did you not sell any of the basses 1-7 ?
From your description it does not sound like you're doing much with them.