Hello,
HikaMarket send a notification email to the vendor for its sales ; and that email just contains product related to the vendor (so if there are other products of other vendors, the is no information leak).
Now if you have a vendor restriction for the cart and you're using "vendor payment methods", best would be to configure the vendor payment methods with the vendor details. So the customer will know how it should do.
It can be really useful for manual payment plugins like "check" for example.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.