It's one thing to quote someone over the phone a price to plant a few flats of annuals, but for everything else that takes face to face time and you are giving professional recommendations you should be charging for your time. But the other guys in town all give "free estimates" right? You can either sell the client on the fact that you have the experience and are taking the time to give them the best information rather than a fly by night operation desperate for work. You can even credit part of the consultation if you are hired. Either way you time will be coming out of someone's pocket. Why not the people's pockets who didn't hire you rather than your existing clients?