**When you open a short position, you sell borrowed shares and receive the sale proceeds. A market short-sale order normally fills against buyers’ bids, starting with the highest available bid.** The ask prices matter when you buy shares—including when you buy back shares to close the short. The $2.50 last-sale price records a previous trade; it does not guarantee your execution price. [SEC’s explanation of order types](https://www.sec.gov/files/trading101basics.pdf)

Borrowing and selling are separate parts of the transaction. Your broker arranges a loan of **1,000 shares**, and you owe **1,000 shares back**. You don’t purchase those borrowed shares at $2.50 each. Borrowing fees and margin requirements apply separately from the price at which you sell them. [Investor.gov’s explanation of short sales](https://www.investor.gov/introduction-investing/investing-basics/how-stock-markets-work/stock-purchases-and-sales-long-and)

Your ask-price example therefore doesn’t provide enough information to price the opening short sale. Suppose the **bids** were:

| Buyers’ bid | Shares available |
|---|---:|
| $2.50 | 500 |
| $2.40 | 250 |
| $2.30 | 250 |

Assuming those bids remain available and no short-sale price restriction applies, a market order to short 1,000 shares could fill in those three parts. You would receive **$2,425**, an average of **$2.425 per share**, before costs. Each portion has its own execution price; the first price does not automatically apply to all 1,000 shares.

Conversely, if you were **buying back** 1,000 shares against your stated asks, the fills could be 500 at $3, 250 at $3.50, and 250 at $4: **$3,375 total**, or **$3.375 per share**. These examples assume the orders remain available while yours executes. A sell limit order lets you specify the minimum acceptable sale price, but some or all of it may remain unfilled. [SEC’s explanation of market and limit orders](https://www.sec.gov/files/trading101basics.pdf)

As for being unable to short, **there’s no single useful frequency**: it depends on the stock, quantity, broker, and conditions at the time. Your broker generally must locate borrowable shares before executing the sale. Insufficient borrow availability can prevent the trade, and account or broker restrictions can also apply. Brokers may identify shares as “easy to borrow” or “hard to borrow”; check availability and the borrowing rate for your specific order. [SEC’s locate requirements](https://www.sec.gov/investor/pubs/regsho.htm), [Schwab’s short-sale terms](https://advisorservices.schwab.com/legal/schwab-one-account-agreement)

One exception to the normal bid-side execution: after a qualifying 10% daily price decline, U.S. Rule 201 generally restricts short-sale execution at or below the national best bid for the remainder of that day and the following trading day. That can keep a short order from filling immediately. [SEC’s explanation of Rule 201](https://www.sec.gov/investor/pubs/regsho.htm)