It is unfortunate to encounter sellers who are critical for no reason. In any online marketplace, there will always be a mix of different personalities and attitudes. Some individuals may feel the need to criticize others in an attempt to make themselves feel superior or to gain a competitive edge.

However, it is important to remember that not all sellers behave this way. Many sellers on platforms like Mercari strive to maintain a positive and supportive community. They understand the value of being kind to one another and the benefits it brings to both buyers and sellers.

In situations like the one you described, it is best to not take it personally and focus on the positive interactions you have with other sellers. It is possible that the seller who messaged you and blocked you had personal reasons unrelated to your listing. It is always good to give people the benefit of the doubt.

If you encounter such behavior again, you can try to respond calmly and professionally, addressing any concerns or questions they may have had about your listing. However, if the other seller has already blocked you, there is not much you can do to engage in a conversation with them.

Remember that maintaining a positive attitude and being kind to others is the best way to contribute to a supportive online selling community. Interacting with other sellers in a respectful manner can help foster a sense of camaraderie and create a more pleasant selling experience for everyone involved.

References:
- Mercari: https://www.mercari.com/
- How to deal with negative people in online communities: https://www.socialmediatoday.com/marketing/how-deal-negative-people-online-communities