Tracking is quite expensive and the postal system is very reliable.
If your seller's Detailed Seller Ratings show 4.8 or better for Shipping Time, you probably will have no worries.
If your item is expensive ($100 or more) the seller may use a Delivery Confirmed service. Some of these include tracking, but since the purpose of the tracking is to allow the seller to prove to Paypal or eBay that the buyer has received the parcel in case of a dispute, there is no reason for a buyer to pay extra for it.
Extra can mean charges of $20 or more, depending on the service used.
Is your item past the time you would have expected to have recieved it? Generally, allow 20 days for arrival from Canada or the USA, 15 days from Europe, and 30 days from Asia.
If this time has gone by, on a weekday, contact the seller and ask for the Delivery Confirmation number, the service used and the date shipped. No DC number is not a problem, you want a prompt reply and at the least the date of shipping. If you don't get a satisfactory response, start an Item Not Recieved claim with eBay. You have up to 45 days for this.
Oh, and don't accept a"replacement" it won't arrive in time. Go for cash.
