Terrible idea. Buyer would get only “I best, order plz” offers.
You can send up to 10 offers every day. Choose requests wisely (that is, only the ones you can fulfill well), and send well-written offers that will convince the buyer that you’re the best one for the job.
Buyers have the right to hire whoever they want to hire. As a seller, you have the same chance as everyone else.
By the way, in your business card gig, you’re using templates as pictures. Have you bought the rights to use those templates? If you have, you might want to mention that in your gig description, otherwise buyers might think that they’d get stolen goods from you; even better, use only the pictures of the business cards you’ve designed from scratch, and show the buyers what a great service they’d get from you.