Mercury rules 12th and 3rd house is in 7th house in Capricorn

When Mercury is placed in the 7th house of a native's horoscope in the Capricorn sign, it can indicate intelligence, communication skills, and business acumen. This placement can make the native very practical and disciplined in their approach towards relationships and partnerships.

However, they may also be prone to being overly critical and demanding in their partnerships. These individuals may place a high emphasis on the importance of education and intellectual pursuits in their relationships, and may seek a partner who is intellectual and ambitious.

Since they have good communication skills, they are able to articulate their views and opinions very clearly, thereby making them very persuasive in their approach towards others.

Overall, Mercury in the 7th house can be a favorable placement as it can bring success in business partnerships and collaborations, as well as harmonious and communicative relationships. However, it is important for the native to work on their tendency to be overly critical and demanding in their approach towards their partner.