There is a method which is true, but it only works to check if someone DELETED you (NOT BLOCKED).
Go to Tools => Options => Privacy.
If you blocked the contact you're checking, go to the right list, and right-click on the contact. If the option Delete is enabled, this contact deleted you. If it's not enabled, this contact has you in their contact list.
If you haven't blocked the contact, go to the left list and right-click on the contact. If the option Delete is enabled, this contact deleted you. If it's not enabled, this contact has you in their contact list.
Delete enabled => You can click on "Delete"
Delete disabled => You can't click on "Delete"
Also, click on the button under both lists, where it tells you who has you on their contact list.
Note: delete is not the same as block. someone might have you on their contact list, but they may have blocked you.
Note: I have tested this with my friends and Polygamy, and it's 100% true.
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