The 3rd house is the house of courage, siblings, and self-effort. It is the natural house of Mars. Mercury (Budh) is the planet of trade, commerce, and intellect.
When Mercury sits in the 3rd house, it is considered highly detrimental for business. The aggressive, impulsive energy of the 3rd house (Mars) clashes with the calculating, logical energy of Mercury. The person will make impulsive business decisions, trust the wrong partners, and lack the patience required to build a stable enterprise.
As a result, they will face constant losses ("nuksan") in trade.
🪔 The VAYOM Remedy
If you have Mercury in the 3rd house, avoid independent business. You will find much greater success in a stable job, administration, or consulting, where your intellect is used without the risk of financial ruin.