The only eBay rule is, that everyone would have a chance at the free shipping..and they would, they just have to pay a certain amount for the item.
The only reason I don't care to do that, is I'd be paying eBay fees on the shipping. But yes, it does seem to interest people when something is free. I've seen it right in the title, and then when I open the auction, the next words are..if bidding goes over $30 (or whatever amount).Here are eBay's rules on promotional shipping. Not exactly what you want, but close enough I think:
Promotional Shipping Rules
You can choose from three options to create a promotional shipping rule. This rule will apply to all listings with shipping discounts (whether the listing has flat shipping or calculated shipping rules). When buyers qualify for your promotional shipping rule, the promotion takes priority over your flat or calculated shipping costs.
Spend a specified amount on 2 or more items and shipping is free or discounted.
Example: You can specify that if a buyer purchases 2 items for a total of $25.00, the buyer receives free shipping. Or you can specify that if a buyer purchases 2 or more items for a total cost of $25.00, the buyer pays only $2.00 for shipping.
Buy a specified number of items and shipping is free or discounted.
Example: You can specify that if a buyer purchases 4 or more items from you, the items will be shipped for free. Or you can specify that if buyer purchases 4 or more items from you, the total shipping cost will be $2.00.
Charge a maximum shipping amount for a single order.
Example: You can specify that a buyer be charged no more than $5.00 for shipping if the buyer purchases more than one item from you.