I purchased my missus Zafira GSi Turbo on ebay without seeing it first. Not something Id recommend, but if its a bargain, and you dont want to travel long distances to see it (for risk of being outbid and your journey for nothing) then what others have said is right.
When we bought the Zafira we asked LOTS of questions, and he described some faults through e-mail correspondence that he hadnt made mention of on the auction description. Word of advice here - better to do this via e-mail than phone, so you have record of all the description and answers the seller gives you, in case it doesnt match the description when you go to collect.
The car was in Plymouth, some 3-4 hrs drive from my house, so I wasnt really wanting to make an extra trip to view the car if I could avoid it, and as I managed to get it some £3k less than comparable models were being advertised for, it was worth a small gamble.
If the seller insists on a holding deposit before you can get to see the car, get them to agree up front (again through e-mail) that the deposit is refundable if the car is not as described. If the seller has nothing to hide, they should agree to this fine. If they dont then it may indicate that they are aware of some problem theyre trying to hide, so beware!
I took the Zafira for a good test drive BEFORE handing over any payment, to ensure it drove as well as he said, also did a HPI check on the VRM, and thoroughly checked all the paperwork and history before handing over the bankers draft. Make sure you get the green slip off the V5 also, as Stu suggests, if you can find someone local to the car wholl meet you and give it the once over, so much the better.
There are lots of honest people selling cars on ebay - Im one of them having sold 3 cars now, and bought 1. I had nothing to hide, just didnt want the hassle of spending £50 for a 3 week ad in AutoTrader, and worrying what might happen if the car didnt sell in that time, and Id have to try dropping the price, and shelling out another £50 to extend the ad. On ebay, you can be sure youll sell the car in 10 days from auction start, and if you need the car gone (i.e. already bought a replacement) then its the best way to move it on, plus you are not penalised for a long ad, and can fully describe the car rather than having 3 lines in Autotrader to try and cram as many acronyms in as you can!
BUT!!! There are also some dodgy traders on ebay - people who have stolen, crashed, clocked cars, or people who want to shift something quick as a major fault has developed and they want it gone before it goes pop, which means you have to be careful, and make LOTS of checks on both car and seller.
If youre careful, you can get a bargain, and also find it an easy way to purchase a car - saves haggling with the seller!
Use your common sense, and youll be ok!
Cheers & good luck,
Dave