One of the best things you can do to build trust is to be honest about your shortcomings. No product in the world is the best for everybody, and the customers know it.

Be straightforward about your weaknesses and mention which competitors can offer the value that you can't.

I'm sure you know the famous Listerine ads from the 1970′s that said "the taste you hate, twice a day". When the competing product Scope was touting it's great taste, Listerine people responded by admitting the terrible taste - and making a point that it's a necessary trade-off to achieve the superb effectiveness.