I've installed a valid SSL certificate to reseller's panel:
RCC > Top > Configuration Director > Miscellaneous Settings > SSL Setup > Certificate
This SSL certificate is used for securing store:
RCC > Top > Configuration Director > Miscellaneous Settings > SSL Setup > Summary tab : Store = Enabled
But provider's SSL certificate is used when I open store URL. Why?
The reseller uses provider's IP Address:
PCC > Top > Account Director > Reseller Manager > Resellers > %reseller% > Hiding
Server Name: %store.reseller.pbas% Server IP Address: Share provider's IP Address
It's by design of Apache that SSL certificates are installed to IP Addresses not to domain names.
Setup a dedicated IP Address for the reseller. Here you may find more detail about Hiding Reseller's URL.
Note: It may be required to restart httpd for the changes to come into force.
# service httpd restart