There isn't an unlimited supply of buyers who are willing to pay the really high end prices so if too many more of the same thing come up in a row then each time one sells the amount the buyers are willing to pay can slide lower.
I used to believe that as well, but it seems that now, seeing one sell for $350+ justifies the price for the next one - I wonder what this auction for a NIB 5300 plus 8 rooms of furniture will close at, $600+, maybe?
Update - sold for $830http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220499542918It seems that the prices for playmobil on Ebay have gone up quite a bit in the last 3 monhts. Here's a pile of junk selling of over $100.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230390644992. Maybe there's something really rare included that I'm not aware of, but it looks like $40 worth of stuff on a good day.
And trains! Just look what trains have been going for:
a 4005 (green loco passenger train) for $232 + $35 shipping.
a 4024 (frieght train) for $212 + $35 shipping.
or a 4010 (cargo train) for $224 + $30 shipping - last year these were $164 at playmobil.com with free shipping!