I'm in New Zealand, which has similar UK based laws, and here if you make a factual statement, and have the proof that such a statement is factual, then while yes you can be sued, showing the court the proof of the statements made will get the case dismissed.
They need to prove that your statement is false for it to be libelous or slanderous. stating facts when such facts are true and provable is neither slander or libel.
For instance, stating Dealer X charged $Y for item A, while Dealer Z charged one quarter as much, so you will not be using Dealer X anymore as his prices are too high, if you have the reciepts that say one item which is identical to the other item bought in two places and one if 4 times the price of the other... that's a truthful statement.
If you just say with no proof that Dealer X is a rip-off artist, don't buy from him... then yes Dealer X could claim libel if you are unable to provide any proof beyond your own opinions.
Under Westminister law, which the commonwealth bases a large part of their common legal basis upon, A truthful, provable statement of fact, is not libel.
Disclaimer: I did classes in prelaw and law of contracts as part of my studies for a business management degree, but I am not a qualified lawyer.