Often times Rahu gives bad results it’s all due to the unfavorable positioing of Rahu in chart, thereby there are some unfavorable positions of Rahu which are considered bad these are;
If Rahu is positioned in the 6, 8, 12 houses, these are Trik Bhava and Rahu is considered weak or bad to deliver auspicious results.
If Rahu is getting the unfavorable aspects from the enemy planets e.g. Sun, Mars, Moon, Jupiter then Rahu looses it’s powers to deliver good results.
If dispositor of the Sign occupied by Rahu is having low score in Ashtakvarga then this factor harms Rahu to deliver good results.
When Rahu gives good results
Rahu considered as good in Taurus, Gemini, Capricorn, Aquarius signs and if it’s dispositors are also in the well state then Rahu gains strength and delivers good results.
Houses of growth (Upachaya Houses) I.e. 3, 6, 10, 11 are considered as the good houses for Rahu and Rahu delivers it’s good results while posited in the above houses.
On the other hand favorable Mahadasha to Rahu also increase Rahu’s suspicious results delivering capacity.
I hope this help you to understand it better.