You need to ask yourself several questions.
1. What does that $20 represent to you? Is it a few drinks at Starbucks? Or is it a coouple days groceries?
2. Do you want to be sure you get a copy without the smudged pages (pp140-141? If you buy it in-store you can check it out.
3. Do you want to wait a week to be able to read and use the MM?
4. How much does the FLGS mean to you?
If $20 is a lot of money, you should wait for Amazon.
I don't know the percentage of faulty books, but I was told of a store that had received 72 bad copies (they seem to sometimes appear in batches) Getting a bad one from Amazon can add a few more days before you can use it.
If you need the book now, you have your answer.
Regardless of timing, your local store may be important to you, or it may not.