Modules upgrades are free within the same cart branch they were purchased for originally. For upgrades between cart branches the cost is 25% of the original price. Installation service for modules upgrades is not discounted.
MySQL 5.7.x installs with "ONLY_FULL_GROUP_BY" sql_mode active by default. With this MySQL option active X-Cart 5.2.x fails and throws an error with the famous orange Oops! screen: An exception occurred while executing 'SELECT x0_.moduleID AS ...