Contracts-Offer & Acceptance: Multi-state Nuances

Some things I learned from PMBR on contracts:

The mailbox rule for acceptances doesn't apply if the language of the offer tells you to accept by "notifying me by Friday." If you deposit an acceptance in the mail on Wednesday, and I revoke the offer on Thursday, before I receive your acceptance, my revocation is effective. Only "notifying me" was an acceptable means of acceptance. Mailbox rule doesn't apply.

An offer manifestly made to too many offerees (2 tickets offered to three different people) is not an offer unless there's a first come, first serve provision.

Power of acceptance destroyed by:
--revocation (at any time before acceptance)
--lapse (if offer has time-stamp or reasonable time; rule of thumb is that offer made in conversation lapses at end of conversation)
--rejection/counter-offer (but "mere inquiry" isn't a counter-offer)
--death/incapacity (of either party before the K is formed)

BUT remember that offers are easily revived by the offeror.

The general rule is that silence cannot be construed as acceptance with 2 execeptions:
1. prior dealings make silence a reasonable acceptance.
2. if you knowingly take the benefits in silence, then you have accepted (e.g. watch them put the pool in your backyard).

Under the UCC, non-conforming shipment is interpreted as acceptance and simultaneous breach. Exception: if the seller promptly notifies that shipment is not acceptance but accommodation only.

Under UCC, you can accept by: promise to ship, ship, or ship non-conforming goods.

If there are identical cross offers, there is no meeting of the minds and no contract.

Indirect revocation: offeree acquires reliable information that is inconsistent with the offer's continued validity.

Unilateral contracts (where only performance is an acceptable acceptance):
--right to revoke is extinguished with beginning of performance
--acceptance comes only with complete performance
--mere preparations don't constitute acceptance or destroy the right to revoke

Question/contradiction: on page 18 of the PMBR contracts outline, the rule states that in an offer for a unilateral contract, "an offeree who commences performance is not bound to complete it." Yet on question 19, the answer choice reads: "As a general rule, where the offeree begins performance contemplated, he thereby impliedly promises to complete it." Seems like a contradiction to me. Any thoughts?