Morally it is wrong. Selling on BassChat means you're selling the bass to a fellow bass player in the (mistaken) idea that they're buying it to play. In a lot of cases you're prepared to let it go for a lower price as you're fairly confident in the above.
If the market place begins to get inhabited by people flipping basses then the bargains will disappear and as a community we will be worse off for it.
Name and shame and don't sell them anything again.
However, if you've said it needs work and have lowered the price to reflect that, the buyer spends a morning sorting electrics, neck relief, action, cleans it, sticks new strings on it and then sells, where anyone else may not have the skills or time (like you didn't) to fix those things, then there's no issue.
In summary, it depends why you let it go for less than the market value.