Just a quick point - I have noticed that many other sellers who have Tesco Clubcard vouchers up for auction are putting the amount you would get in Deals as exactly 4 x the coupons face value (e.g. £16.50 coupons = £66 Dealx vouchers). This is only the case if the amount you have is an exact multiple of £2.50 (e.g. £20 coupons DOES = £80), as Tesco only convert coupons to deals in full £2.50 denominations.
Therefore in the example above, for £16.50 worth of coupons you would receive £60 worth of Deals coupons and the remaining £1.50 would be credited back on to your clubcard.
I hope this helps! :-)