alright.
First - you will need skybank(paypal account)
1st - check the seller's feedback ( click on star beside
the seller's username)
2nd - seller's location ( countries like India,china have many
reported cases that parcel was delivered without items in it )
3rd - check if the seller ships to worldwide.
4th - images provided by seller, ( is it taken by seller or just
copied from google/yahoo images) a original image usually has
different angle views and more then one picture
5th - check if seller enables "money back within 7days or
more service" its much more safer.
6th - read description on item carefully to ensure no
misunderstandings.
7th - check if shipping is over priced ( you can check it on the
official website of the delivery service the seller uses) ( you
will roughly need to know the weight of the item) shipping
details/time can also be checked from there.
8th - if item is on auction , watch the item and place your bid
only at the last few minutes to increase chances if winning bid. If
item is sold in Store inventory , check quantity avaliable before
buying.
It is best that you use the "Ask seller a question" feature that
is available.