Hi,
I invite you to take a look at the HikaMarket product page and his documentation.
You will see that HikaMarket allow to create a full working marketplace and it have a very powerful fee system too.
Now, the web services are still not available in HikaShop (and HikaMarket too, by the way) but the feature development is in progress (once we will have the confirmation from the other party who asked for that development).
It is currently not a blocking element to create a marketplace.
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.