This is information provided by eBay for limiting bids. I found it by going to help and then typing bid limit:

Buyer Activity Limits

Buyer activity limits are one way that eBay helps sellers to minimize Unpaid Items disputes. Based on eBay’s research, more than 50% of Unpaid Items come from new users with a Feedback score of less than 5. The goal of buyer activity limits is to minimize Unpaid Items while supporting legitimate purchases. Under this system, buyers can take appropriate actions to remove their limits:

Buyer activity limits place restrictions on bids or Buy It Now purchases.
These limits will be applied in very rare circumstances.
These limits apply only to new users who have not yet demonstrated positive participation in the marketplace or to existing members demonstrating a highly unusual pattern of buying.
Some Examples

eBay cannot publish the specific rules for its activity limits. However, the following are two examples that illustrate situations in which new members may encounter activity limits (Note: These are not actual activity limits).

Example 1: A new member who has won 20 items totaling $1,000 and is the high bidder on another 40 items in a short period of time may encounter an activity limit.
Example 2: A new member who has won items totaling $5,000 and is high bidder on items totaling another $3,000 in a short period may experience an activity limit.
A member may encounter a limit based on several factors including (but not limited to):

Number of winning bids currently placed.
Number of items won in a short time period.
Dollar amount of winning bids currently placed.
Dollar amount of items won in a short time period.
Amount and dollar value of feedback the member has received for items won.
Number of items for which the member has paid.
Removing activity limits

Members who encounter activity limits can remove these limits by:

Verifying their identity. Accountholders may be given the opportunity to verify their identity by registering for PayPal, using a valid credit card (MasterCard or Visa only at this time), ID Verify ($5), or other options that eBay may offer in the future. Note: Not all members will be given these options.
Receiving positive feedback. Positive feedback is often a good indicator of a member's likelihood of paying for items they have committed to buy. Members who have received positive feedback tend to have lower Unpaid Item rates.
Why does eBay have activity limits?

eBay has buyer activity limits to encourage responsible bidding and buying in order to protect both buyers and sellers from unintentional or malicious “over-buying.”

In addition to buyer activity limits set by eBay, sellers can limit buyers based on certain criteria by selecting buyer requirements. Sellers can also limit buyers based on their User ID (see Managing Bidders and Buyers).