If you click on the amount that is 'Available to spend' on the MultiBit screen it takes you to this help page:
http://multibit.org/help_availableToSpend.htmlIt is the amount that you have in your wallet that has been confirmed by a block.
MultiBit only allows you to spend bitcoin that have been confirmed by the block chain.
If it took 3 days to confirm a transaction then the probably reasons are:
+ the fee for the transaction sent to you was lower than the minimum amount. (Eventally the bitcoin in the transaction 'mature' and the required minimum fee drops and then a miner includes it).
+ one of the amounts that the person sent to you used was unconfirmed and hence your transaction was only put onto a block when the previous transaction confirmed. Some of the other wallets, notably blockchain.info, allows you to spend bitcoin as soon as you receive it (i.e. it does not wait for confirmations).
The transaction confirmation is a bitcoin network thing, not a MultiBit thing.
I personally always set a fee a bit more than I have to to avoid my transactions getting 'stuck' in the system and then the recipient experiences the 'transaction takes ages to confirm' that you have just seen.
In this case what you suggest me to do everytime before making any deal ? any information will be good for me thanks
what should i tell to buyer and also take care of myself !