I am a collector of rare TV shows from the 70s and 80s - and iOffer has the biggest catalogue of these TV shows - it's incredible, they have stuff even I have forgot existed.
Unfortunately, it's a mine-field.
While half the time, the sellers will ship you a decent product - the other half of the time they will either send you DVDs with terrible video quality or sometimes they won't deliver them at all.
In one case, I finally recieved my order, sent from China, 8 months after I ordered!
If it's a TV show you can't find anywhere else, I'd say iOffer is worth the risk.
But if you can find it elsewhere, buy elsewhere.