Well, Here is the truth about ebay turbos.
The are mostly knock off garrett units. They are all going to be unbalanced. Now, You may think no big deal. Wrong, When you have something spinning at 100,000+ RPM, You want the fucker to be balanced. I have only seen a picture of one glued together, Never IRL.
The rule of thumb with an ebay turbo is to not go above 12psi, And don't expect it to last more then 6 months of daily driving/beating. My first ebay lasted for a year, My second was broke on arrival, and my 3rd lasted 4 months.
Turbo specs
My first turbo T3-T4 50 A/R. At 6-7 psi it lasted a year. I killed it once I got my car tuned and pushed it to 12lbs. I still pulled 3 cars on the mustang I was racing at the time though:)
2nd turbo T3-T4 60 A/R, Slapped it on the car and it wouldn't hold pressure.
3rd turbo, T3-T4 60 A/R, I took this one apart and made sure everything was ok. It lasted 4 months at 14lbs, and maybe one spike to 16lbs on a cold night.
I will NEVER buy another ebay turbo, Granted the ones I did buy were 80 bucks, And the 3rd was a replacement for free they still suck balls. They are only ok at best for cars that have stock engines that will never see over 6psi. The only turbo that I will buy now is a REAL Garrett unit. However, there are other well respected companies to purchase from.
The next step is ebay manifolds. I can not say enough about these piles of shit. I have more patch welds on my manifold then a I ever care to think of. I've had my entire wastegate fall off the manifold, Twice. DO NOT EVER EVER EVER EVER think of getting an ebay manifold, Or any cheap manifold for that matter. You are only setting your self up for a lot of work down the road. They will crack, They will need repairs, They flow like shit. In fact, Here are some pictures of my lovely ebay manifold.


PILE O SHIT.
Ebay intercoolers are the one part you can buy with out to many problems. Unless you plan on pushing over 400whp they do just fine. Just buy from a seller with good rep. I have one on my car, Its beat to shit, been in 3 front end wrecks, and mowed down a possom at 80mph. Still no leaks.
To learn about how turbos work, click these links.
Turbo 101
http://www.turbobygarrett.com/turbobyga ... ch101.html
Turbo 102
http://www.turbobygarrett.com/turbobyga ... ch102.html
Turbo 103
http://www.turbobygarrett.com/turbobyga ... ch103.html