We've done that at the main Auto Assembly convention for two years now and it seems to be quite popular. We have asked for a small commission for the convention to help towards our running costs (10% from each sale) but last year we had over 500 items on the sale ranging from brand new items we got in specially for the table, rare Japanese G1, Binaltech, comics, DVDs... a really good mix.
This year, we've only just started promoting the table but we should have about 100 items ready for people to pre-order by the end of the weekend, possibly including a Lucky Draw toy!!
It does work really well though, and it helps raise funds for the convention too!