One thing I hate is the free for all attitude with lefty vintage basses. There are guidelines for the great majority of the righty bass world for value and they set the bar for the value of vintage pieces one way or the other, but the unmonitored (or ignored) faction of the vintage instrument market that's left handed seems to be an invitation to many sellers to play fast and loose with their pricing.
Where a righty bass is valued at $3000 in the price guide might typically range a few hundred dollars in either direction, a left handed example of the same bass priced at $3000 for it's right handed counterpart could suddenly fluctuate in price by thousands.
I recently had a '71 Precision offered to me that had been entirely stripped of it's original finish. I consulted the vintage sellers I know and asked for opinions about the bass on BABP. The general consensus was the bass was worth about $1800, due the the fact that generally a stripped instrument gets devalued by half, and they priced it at $400-600 more for being a lefty. So I told the seller that was what I thought was the fair price, told him why and even gave him links to where it was discussed. He was deeply offended, certain I was trying to lowball him, and based on what he saw online and some funny math deduced for what the mint right handed examples go for told me he was certain the bass was worth $3000 and not a penny less.
This would have been a simple matter if the left handed version was listed in the price guide, but instead the inflated value perception of lefty stuff had him thinking wild prices for what amounted to a nice players bass.
While it's true left handed stuff is more uncommon, so too are lefty players. The demand has to match the availability, and the flawed notion that the rarity of lefty basses makes them command whoppingly higher prices has probably cost most of us more for an old bass at some point.
We need to do our own Lefty Vintage price guide! I wish...