Accept vs. Except: Make No Acceptions

Thanks to Meg for calling my attention to this homophonic blooper on Marriott's website:

Valid seven days a week accept at Coronado Island Marriott Resort & Spa and The Lodge at Sonoma Renaissance Resort & Spa where the offer is valid Sunday - Thursday.

Oh dear. Third graders across the land are wincing and mocking.

Where does Marriott go wrong? It mixes up the homophones accept and except, and it does not use a comma to set off a non-essential clause.

Quick rules:

• Accept is a verb meaning 'to receive.' Except is a preposition meaning 'but not' or 'with the exclusion of.'
• Use a comma to set off a non-essential clause (also called a non-restrictive clause). This is a clause that adds information but is not essential to the sentence's meaning. He left his book at the library, where he had spent the afternoon. The essential clause could be a sentence on its own: He left his book at the library. The non-essential clause adds information but could be removed without changing the meaning of the sentence.

Correction:  

• Valid seven days a week except at Coronado Island Marriott Resort & Spa and The Lodge at Sonoma Renaissance Resort & Spa, where the offer is valid Sunday through Thursday.