Do asphalt contractors throw away unused sealant at end of season?
This is the setup for a classic scam. The offer might be legit, but that is really not the way to bet. Before pursuing this check with the police, BBB, att'y general's office, and past customers.

http://www.bbb.org/blog/2012/04/watch-out-for-paving-scams-this-spring/

[H]ere are a few red flags that you can look for in a driveway repair scam:

* The contractor says there are leftover materials from another 
job – Professional asphalt contractors know, with great accuracy,
how much paving material is needed to complete each project. 
Rarely will they have leftover material.

Scammers use this as a ploy to explain how they can provide you
with a huge discount over the normal price. The catch is that
they will ask you to pay everything upfront. The materials tend
to be inferior and the work ends up shoddy.

* Beware if you are pushed to make a quick decision – Trustworthy
contractors will provide a written estimate that will be valid
for days or weeks. It should specify in detail the work to be
performed and the total price.

* Be suspicious if you are asked to pay on in cash – Most 
reputable contractors will take checks or credit cards.

* Watch out for a company that is from out of state – Look at the
truck the representative travels in. If it is unmarked or has an
out-of-state license plate, be cautious. Even if the
representative claims to have a local phone number, scammers can
easily purchase disposable cell phones to provide a local number
in the area they are soliciting.


Or just websearch "driveway scam". Sometimes it's repaving, sometimes it's resealing, always it needs to be considered questionable. If an offer sounds too good to be true, it usually isn't true.