No. The Devs Wanted category is for saying that you want to contract specific plugins. The actual negotiation, transaction, etc takes place outside the forums, and the money goes towards developing a new plugin, not paying for your copy of an already-created plugin. There's a key difference between selling your goods and selling your services, especially since each additional copy of the good costs nothing to produce. It also has the potential to bring in flak from Mojang, if they ever decide that 'Minecraft mod' can also mean 'Minecraft-interfacing-software mod'. There is in fact a forum called Devs Available which allows developers to advertise their services.
I would also say that the ability to directly sell plugins has contributed significantly to the toxicity of Spigot's community, especially since you'll see a lot of their authors asking basic java questions on the forums right after, and the decompiled plugin jars containing verbatim example plugin code.