Who should pay the transactions fees? In traditional transactions, the merchants pay the fees. For bitcoins, it seems that the payer is paying the fees. In pratice, what will happen for a real transaction? If the payer does not enough fees, the transaction won't be confirmed. Or should the merchants include the transaction fees in the price?
In Bitcoin it is indeed the sender who pays the fees. Also for "real transactions" (with the marginal case of P2SH where one can say that the receiver pays part of the fees upon spending the proceeds of the P2SH transaction).

Indeed, if fees are too low, the transaction is not confirmed. Therefore, the seller typically waits to see whether the transaction is confirmed before delivering anything.  

At present the fee is typically less than USD 0.1.  

Because the fee necessary for a transaction depends on the length of this transaction (ie its number of inputs, among other things - something determined by the buyer's history), it is hard for the seller to specify a fee that applies to all the expected transactions.The transaction fee can therefore be seen to be only implicitely and approximately included in the price.