Dodgy Ram Suppliers?, Which ram should I get? Options

[FallaciousUltimatum]

My mumma is going to buy me some ram for christmas.
I have an oldish imac which has some crappy bus speeds, and only 1 Gb ram.

Anyway I'm looking for a 4GB (2x2GB) upgrade, my mum was going to pay the stupid apple people $300 to install it and 'surprise' me for christmas!
But thankfully, she didn't get the chance to do it before christmas. I cracked it when mum gave me a homemade voucher for christmas

"More Mac
Ram - 4G's
for
Tristan
Tues. 30 Dec.
B there
Computers Now
High St,. Malvern"

I was like MUM! HOW MUCH DID YOU PAY FOR THIS!
I can buy it and pop it in like a SD card for under $100!

Then she was all like, oh the warranty! You'll break it!

Whilst maintaining my cool around the family, I ran over to my computer, used my brand new screwdriver and pulled out the current ram.
So know even if pulling out the ram voids the warranty ( ) it is already being done.

SO NOW I NEED TO BUY SOME RAM OFF EBAY!
240 Pins, 667MHz, DDR2, SDRAM, 2x2GB

Most of the ram I've looked at has been $90-$160
But all the ones here look incredibly dodgy and only $40-$80

Ebay Listing

Could someone please explain why these are so cheap?

And tell me which one to buy!

Thanks for the help

Tristan