Hello,
When a guest is adding a product in the cart ; that information is stored in the database and link to his session.
You can consider that, after several days, the session has expired and that you can delete the old carts.
That's all we are saying.
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.