Serrotta sounds a good way to start if you a new to this and spending a lot of money on the bike. Might be worth the price if it prevents you from getting stuck with the wrong size.

For everyone else........I agree if the bike shop has a limited selection of sizes be wary that they will try to sell you what's in stock.

But honestly, if you are buying a sub $1000 bike I don't see them spending 2 hours with you?

Ballparking it as long as they are honest shouldn't be frowned upon if it is an entry level bike. What new guy is good enough to communicate what he is feeling to the "fitter" in order to get the settings spot on?