Hi,
there doesn't seem to be an option for that, but you can override it by going to "Display -> Views".
Select the view "checkout" and your template, there you will find the view "terms" where the input box is defined on line 11:
<input class="hikashop_checkout_terms_checkbox" id="hikashop_checkout_terms_checkbox" type="checkbox" name="hikashop_checkout_terms" value="1" <?php echo $this->terms_checked; ?> />
You could replace the part
<?php echo $this->terms_checked; ?> by
checked="checked", then the checkbox will always be checked.
Hikashop actually stores this setting whether the terms are checked in the user's session so that if a user goes to another page and comes back to the terms, it will remember whether the box was checked or not, which it won't with the above solution. So if you want to remember the user's setting (which is probably not that important in this case since the user needs to accept the terms anyway to continue) but you could, instead of forcing the checkbox, set the session variable by adding something like this before line 11:
<?php
$app = JFactory::getApplication();
if($app->getUserState( HIKASHOP_COMPONENT.'.checkout_terms')===null){
$app->setUserState(HIKASHOP_COMPONENT.'.checkout_terms',1);
$this->terms();
}
?>
Hope this helps. Kind regards,