Is it possible to limit the trolling access of an IP to a couple of hours?
Can the sign up page link/direct the new member straight to the Intro section? Or to a page first that welcomes them and includes a guide to writing an Intro?
Can there be some sort of block on posting before an Intro is posted?
I have no idea what your on about with the first point, but I can't really limit IP address access from guests because that would block important "trolls" such as the Google bot crawler that indexes the site and makes it findable in Google search results

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Your second suggestion is something that's been on my mind for a while. Improving the sign up flow, to be honest the forum software like most package forum software doesn't lend itself too well to customisations. Notice how I always blame the software?

On a serious note though I should be able to find the language files that are used when people sign up and hopefully change the welcome email to provide a good starting place for new members.
This welcome email could provide 5 or so quick points for joining our site like 1. It's a good idea to write an intro post. 2. Don't talk about sheds. 3... etc...

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I could limit newbies to the intro section, but I think a welcome email might be the best solution.
Yer, sorry bout that 
LOL when I had food poisoning a month or 2 ago I felt dreadful. Damn shell fish, never again. I couldn't even use a computer.
From observation I can say that "sniping" didn't change very much... Instead there has been an influx of useless posting to boost up post counts.
Agree, and I imagine it wouldn't change much at all really.
On the bright side the catalyst for this discussion turns out the person who bought the item really did need it and has now become more active so there you go.
At the end of the day if you want to sell something privately you can always contact people in the club you know and offer it to them first. Many clubs do this to prevent those pesky 16 year olds buying their pride and joy and driving it into a tree lol...