I guess it depends how big you are (revenue size). I don't trust the sales work to anyone but myself; but I understand if you grow to be a large company you would have to delegate the sales process.
You might develop a "tiered" system. I don't care how large my company is, I would not allow anyone other than myself to give final approval to a sales offer that would be more than say, 5% of my annual revenue. In other words I would have control of any offering that could severely effect my bottom line. But you could allow your sales people to price the typical yard, commercial account. My guess to do that is that you would have to have a person that had been with you long enough to trust or someone that you recruited whom you personally knew. I would give them small accounts to price and then go in behind them and see if they are on the mark with the pricing. "Delegate" but then check behind them. Even if you develop a plan with pricing per sq ft, you have to check behind them because there is some talent associated with pricing that way too. Are they lazy? Do they understand the computations? Do they have enough common sense to know they have to subtract the size of the house & flower beds from the sq ft of the lawn. I know this sounds basic, but a typical sales person does not necessarily have common sense, especially if they are commission driven (larger sq ft + more $).