Two quotes for the same lot can differ by forty percent and both be honest. The gap is almost never profit margin — it is coverage rate, surface preparation and crack treatment. Those three items decide whether you buy four seasons of protection or one.
Coverage rate is the whole product
Commercial sealer is sold by the litre and applied at a measured rate per square metre. A two-coat application at a documented rate uses roughly double the material of a single thinned pass. On day one both lots look identical black. By the following spring one is worn through at the drive aisles and the other is not.
Preparation is where the hours hide
Sweeping, blowing, oil-spot priming and edge trimming are labour with no visible product attached, so they are the easiest hours to remove from a bid. Sealer applied over dust does not bond — it lifts in sheets under the first winter's plow.
Crack treatment separates the two prices
Routing and hot-pour sealing a working crack costs real money per linear metre. Painting over it costs nothing. The lot that skipped it takes water into the base all winter, and the following year's repair is structural, not cosmetic.
The short version
Ask every bidder for coverage rate, preparation scope and crack treatment method in writing. If the low bid will not put those three in the document, the difference in price is the difference in scope.