It’s more likely that a spammer has acquired your email address from somebody else’s address book on an infected computer, possibly a friend or other contact you have. They also harvest email addresses from website guestbooks. The spammer will then fake the headers in the spam email to make it look like it came from you. The reason they do this is because you are more likely to open and read the email if you see it has come from your own email address or another familiar address. The odds that anyone would actually purchase something from somebody who uses this scam is almost non-existent. But the spammer / scammers will try anything.