I was already using the same method before.
Why ? Because it's a choice and I feel that
it provide better customer service than removing
cels immediatly :

I have far too many customers that want to ask 
questions before buying a cel, whatever on it's 
condition, price or way to ship it.
Those questions need to be answered and the order 
confirmed before the order is completed.

The only other method is to do like Taro : Force 
people to register and login and then make that 
you have to buy any cels that you put in your 
basket. But that mean no more questions about the 
cels or the transaction., no more trade, no 
more...

So yes, the price for more freedom when ordering 
is that from time to time, you may try to buy a 
cel that someone already ordered just before.
Not everybody is like you and for many people it's 
not the end of the world. 

Cheers,
Yann Stettler