بسم الله الرحمن الرحيم
As per Hadith, bida’h is deviation. Hence it is helping in sin to sell and publish the books which deal with bida’h; hence you should avoid it. The income which is received through it is not completely pure and free of doubt.
ما قامت المعصية بعينه يكره بيعه تحريماً وإلا فتنزيهاً (در مختار مع الرد 9/509 زكريا)
Allah knows Best!
Darul Uloom Deoband