Is it permissible to write reviews for products and profit from them based on online research without personal experience, provided there is a disclaimer clarifying this?

It is permissible to promote products and websites that sell them, provided they are lawful. This falls under permissible brokerage. Evaluating items is considered testimony, and thus requires knowledge and truthfulness. It is not permissible to evaluate something one has not examined, based on the Almighty's saying: ﴿إِلَّا مَنْ شَهِدَ بِالْحَقِّ وَهُمْ يَعْلَمُونَ﴾ (except those who bear witness to the truth, and they know) and ﴿وَمَا شَهِدْنَا إِلَّا بِمَا عَلِمْنَا﴾ (and we did not testify except to what we knew). If the evaluation is based on what has been published online, it must be stated that you have not personally examined the product, and this disclosure should be in a place visible to anyone who sees the product.