As it should be John.
Most forums have a rule regarding selling, (those that allow it), that the seller must have created a login, been active for a set period and have posted at least 10 constructive threads and replies to the forum.
Quite fair and stops these 'house clearance johnnies' from circumventing ebay listing fees to get shot of a stack of NOS kits, (which is generalising but oftentimes that's indeed what this is), most, i've seen on other forums start with the introduction, Hi, i'm new to this thing and have been left a stack of kits by my kindly wonderful old granddad and they're not really the kind of thing i'll build etc, they then go on to list in decent detail the kits and say, I really don't know about these things so make offers, next thing you know someone has offered a fiver for that hard to get tamigawafixvell 1/25000 kit of the moon or whatever and lo and behold, this new guy it seems has done his (ebay) homework and knows what it's worth.
You're actually very considerate allowing sale posts given that you run the forum and the shop, Hitchcocks motorcycles, (Royal Enfield spares), run their own forum but state, as a spares supplier we will only allow the sale of complete motorcycles, any parts sale post will be removed! to be frank, I don't believe thats unfair, (i'm not suggesting you change the ruling, this forum is probably the friendliest I know for models and works very very well as is)