Keep in mind when mentioning things like yard sales, most people don't claim money made from things like yard sales in their income taxes. By accepting the credit card payment you are creating a paper trail and may need to account for that come tax time.
The $1000 weekly limit seems a bit excessive, but their logic of wanting to ensure that your account can cover chargebacks etc, makes sense. I suppose this is the trade-off for not having to have a merchant account and terminal fees, etc.