OcUK state a 14 day warranty period with 'B' grade stock. I understand that legally they have to honour the full 12 month warranty.
The 'B' grade stock used to be really good value, I remember buying a top of the range MSI 939 board that included a wireless adapter for £17 - the board was brand new and came boxed with all of the accessories, the board retailed new for £100+
I've had in total of 6 'B' grade motherboards, 4 worked, 1 was faulty and the last one had bodged soldering work done to the dimm sockets, if I'd powered it up with the memory in etc. it probably would have caused quite a bit of damage.
I find that a lot of the 'B' grade stock is now overpriced and isn't always worth taking the risk. I only tend to buy if there is at least 50% of the retail price of a new item.