For The Most Part, Your Personal Experience With Ebay Will Likely Determine Whether Or Not You Choose To Purchase Tickets Through Their Site. I Sell A Lot Of Tickets On Ebay, And Can Tell You That There Are Many Very Reputable Brokers That Do The Same.

If You Do Decide To Purchase Tickets Through Ebay, Always Always Always Buy "Hard" Tickets!   Never Buy Ticketfast Or Other Types Of "Print At Home Tickets".  While They Are Becoming More Popular And Common, They Are Simply Far Too Easy To Duplicate As They Are Delivered To The Original Buyer In .pdf Format.   Even If You Have Thoroughly Researched And Are Satisfied With A Sellers Feedback, You Do Not Know Where They Got The Tickets From - They May Have Purchased Them On The Secondary Market Too!

Always Use Paypal If You Purchase Tickets Through Ebay - Always!   Ebay Has Become Very Buyer Friendly Recently, And Paypal ( Owned By Ebay ) Has Followed Suit. A Purchase Funded Through Paypal ( Especially If Funded Through A Credit Card ) Is As Safe As Any Other Purchase You Make Through A Credit Card - If The Seller Does Not Produce What You Purchased, Your Funds Will Be Returned.

You Will Find That Tickets Are Listed By Two Basic Groups - Individuals That Just Happen To Have A Pair Of Tickets That They Can't Use ( You Will Find These Are Typically The Tickets Available At A Lower Price ) And Brokers. 

I Always Use The ~Ask A Question~ Link From A Listing That I Am Interested In Just To See How Long It Takes The Seller To Respond, And Whether They Seem Responsive And On The Ball In General.

Whether The Listing Has A Buy It Now Option, Or Is An Auction Format ( Even If It Has Bids ) Don't Be Afraid To Make An Offer On A Pair Of Seats That You Are Interested In. I Frequently Field Offers, And Rarely Have A Pair Of Tickets Listed That I'm Not Willing To Lower A Bit.  Make Sure That You Mention That You Will Pay Using Paypal, And Will Do So Immediately.

In The Case Of Non Brokers, Obviously You Want To Check Their Feedback ( I Won't Even Look At A Listing If The Seller Does Not Have At Least A 99% Feedback Rating ) Just To Be Sure They Are Not "Flaky".   Ebay Has A Decent Tutorial Which Will Give You An Idea Of What To Look For HERE, But Generally, You Want To Be Sure That They Do Not Have A History Of Not Producing What They Sell, And Are Not Users With Little Or No History.  Also, Be Sure To Check Their Other Listings - Including Previous Items ( See How To Do This HERE) If They Have More Than One Pair Of Tickets Listed, They Are "A Broker In Disguise" Which Would Give Me Reason For Concern.

If The Seller Is A Broker, Take A Careful Look At Their Feedback - Especially The Detailed Ratings - This Will Tell You A Lot About Whether They Take Their Business Seriously, Or Are Just In It For A Few Extra Dollars.   Take A Look At Their Other Listings As Well As Previously Sold Items ( See How To Do This HERE) .  If You Are Looking At A $200.00 Pair Of Tickets And The Seller Has $3,000.00 In Inventory Currently Listed, Has A History Of Selling Tickets ( Not Baseball Cards Or Pot Holders ) Has Completed More Than Just A Few Transactions Recently, And Has Very Good Feedback, They Are Probably Real Brokers - People Who Make A Living Buying And Selling Tickets And Take Their Business Seriously. - And I Would Be Comfortable With Purchasing Tickets Through Them.

For An Example Of A Real Brokers Listings And Feedback, Please See My Current Ebay Listings!