Is this considered a professional thing to do or more of a trunk slammer kind of business?
'slammer. There's a whole section on it in the classic reference "Tools of the Trunk" Chapter #2 - Eyeballing and Guesstimation:
Consider rating your quotes like poker hands. The less detail the higher the hand. For instance quoting only the total number of cameras at a single price point with no other info*, is akin to a straight flush, beatable by only the Royal, "1 Surveillence System $3000". This also helps develop your trade lingo, useful when discussing options in front the customer or even socially with others in the guild.
*Except for Sales Tax of course, see chp 15 "You can't Sell Bricks from a Brick Cell."
But seriously, this low-info technique can be used to great advantage since it:
a) cuts down on unbillable and uninteresting hours spent (spec'ing something that you already have decided what you're making regardless of what they're paying)
b) allows you more freedom in using sliding scale substitution of parts when your quote is 'called'.
The biggest challenge lies in getting good at the estimation aspect. Of course the estimation I'm referring is not the for the typical 3C's, (components, connections or capacity), (although chp 6 "How to quickly judge distances using multiples of car lengths and football fields", is a must.), but rather for the more important 4th C, the Customer and for estimating what is the minimum level of detail needed, for him to sign on the line which is dotted. Remember the quote is the physical manifestation of your relationship to the customer, expressed thru line items descriptions and dollar amounts. So correctly anticipating what they expect to see in your relationship is probably the single biggest determinant of success around.
Addressing John's problems
You're too high and a competitor who has studied the site details and spent a little while calculating this out can underbid you and still profit.
This can happen, and sometimes you don't even know. Other times you do, and when you do you can use your ambiguity in your favor, by revealing your 'wild card' line items, e.g. "That's because CutRateCamera is probably planning on Wodsee, I'm quoting you Axis, go ask them"
You're too low, so you win the job but lose money on it.
This can happen to those who low-bid a fully spec'd job, but should not happen to you, again because of your wild cards. You can splurge a little and 'give it the once-over' now that the job is yours. Then you simply choose the quality of product necessary to ensure your profit level is acceptable, all without any visible deviation noticed by the Customer.