For someone that seems to be doing a fair ammount of transactions, Kagi is a poor choice. However, if you work out what a Yahoo Store would cost you...

$49.95/month (Yahoo Store hosting)
+ 0.5% cut on transaction (Yahoo takes this cut)
+ ~$45/month (Merchant account maint. fee)
+ 3-4% (cut Visa/Master/Amex take per trans.)

...then it may work out in his favor to use Kagi. This all depends on how professional you want to look and how much of your revenue you want to surrender.