Hey there Curtis,

Regarding the appearance of not leaving your clients website
to pay, I think there may be a standard payments option to send
a URL in the payment data to PayPal.  This URL is a graphic that
PayPal uses to customize their website to make it look like there
is a more intimate relationship between the two companies.  

This makes the PayPal process look more professional, like an
important corporate relationship — while also making the idea
of a customer's giving-up sensitive credit data seem less risky.  
With the Pmts Pro plan, your client will actually be handling the
customers sensitive credit data.  Either way, I believe your
client's website should make some sort of statement about
payment security.  We went with the standard Buy Now button
partly because we wanted to assure our customers they did
not have to rely on us (who they never heard of) to have the
technical wherewithal not to be hacked or spoofed.  

You might consider selling your client on the approach where
first you build the standard payments Buy Now thing with
their corporate graphic on the PayPal site.  Then, you can
put the additional time into the more complex and risky
payment technique that makes them look like a Fortune 500
company — or whatever.  This is good for your billing, too.

Good luck!

Jim Rodgers