I want to know what is the most important thing that americans care
about when purchasing online.

My guess: Finding it; easiness of receiving it; perceiving value (i
love buying one song rather than a whole CD with songs i don't care to
listen to); civility (believing the transaction runs smoothly);
promptness,being able to get educated about the product by comparing
to other sellers, price. Well, the most important thing? The process
itself.

Security of payment system

I own 7 websites grossing over $500,000 annually.  The most important
things Americans care about are list below in the order of importance
from highest to lowest.  Understand that what is important is organic.
Which I will explain in and example to follow.

In order for the person to stop and even look at the page selling an
item on the entry page you must have.

1. Photo of the item
2. Price of the item

After the person has qualified the item as what they are looking for,
then the following.

3. Freight Cost
4. How long to ship
5. How long to delivery
6. Do they have confidence the seller can actually deliver what they are promising.
7. You must accept Visa/Mastercard and discover, paypal also accounts
for 20% of our payments.
8. Security is not important at all because online buyers know they
can not verify if the website is secure and just because it say it is
does not matter.  Americans can just call there credit card company
and get credited anything that is fraud with no hassle.  It is up to
the company to refute the evidence.  Americans have absolutly no risk
at all when buying online.  Those who do care a little use paypal
which keeps their credit card info hidden or they don't buy online.

To be noted.

Americans do not ever buy overseas. Unless, they save massive amounts
of money. Example.  The Kopi Luwak is world most expensive coffee.  It
is grown in Java, Sumatra and Sulawesi.  To purchase this item from an
american brick and morter retail store you will pay. $400 per pound. 
To purchase from american internet store $250 per pound.  To purchase
directly from the Sumatra online plantation website $60 per pound. 
This is a rare example of an international website that can have
success.  All others beware.

Let me know if you have more questions.

Thanks

Dave