This may be a non-offensive way to negotiate 
with the seller.  Or slightly aggressive, 
depending on how you word your message.

In essense, casually but firmly ask the seller 
to break down the EXACT shipping charges for 
you, such as:

[1] How much exactly are they charging for the 
actual shipping (be it Priority Mail, UPS 
ground, Express, etc.).  Everyone and their 
mother knows that a package for something like a 
few cels or a plushie can only cost so much (the 
weight doesn't vary enough to drastically alter 
shipping cost).

This is one good indicator to keep the seller 
honest about their shipping charge.  Unless 
they're claiming to stuff the package with tons 
of heavy-stiff cardboard, they can only get away 
with quoting so much.

[2] If the shipping method doesn't cover all of 
their total shipping fee, what else are they 
charging you for?

This could include such things as Delivery 
Confirmation, insurance, or packaging 
materials.  If they are claiming any of these, 
make sure they can put an legitimate amount for 
each item.

If there is Delivery Confirmation, ask for the 
tracking immediately after the package is 
shipped.  If the shipping method is Priority 
Mail, argue that the Post Office provides the 
boxes for free.

[3] What I HATE most is when a seller is 
charging an ambiguous handling fee (I think many 
collectors here know 1 or 2 E-Bay sellers 
notorious for this) without ever explaining why 
or what it actually pays for.  Unless the seller 
can sensibly explain such a handling fee AND 
posts the exact amount BEFORE-HAND in the 
auction description... you have a legitimate 
beef with the seller.

Of course, I'm really narrowing in on certain 
points, but in practice you probably could just 
get away with 1-2 quick questions inquiring the 
seller to break down their overall shipping fee 
for you.  As the buyer, you have definitely have 
a right to this kind of information.  And 
hopefully it will keep the seller honest.