What are the update policies of your tools?
use cases
sales and crm
According to the current Odoo Apps Store policies:​
v.12 and prior
every module bought for the version 12.0 and prior gives you an access to the all versions up to 12.0.
from v.13
starting from the version 13.0, every version of the module should be purchased separately.
bug fixes
disregarding the version, purchasing a tool grants you a right for all updates and bug fixes within a major version.
Take into account that the faOtools team does not control those policies. By all questions, please contact the Odoo Apps Store representatives directly.