If HTML tags such as
<b> show up in recommendations, it is most likely due that tags are included in the implementation as a part of product detail page content. You can confirm this by reviewing the product page implementation.
Nosto strips all HTML markup from product descriptions but HTML markup in any other product field such as name, will show up as escaped HTML.
Data reported for Nosto should therefore be in plain format and any additional HTML content should be removed in the implementation, if possible.