Several reasons why it’s very challenging:
Builds up the site’s usability, particularly if it’s placed on all the pages of the site.
Category pages should link to products with keyword rich anchor texts
FAQ pages linking to site’s important pages
Highlight your top products through sidebar widget
Press release and news submission
Video product review
Link Building and Brand Development
Reverse engineer competitors’ links
Reach out to bloggers and build relationships
Contact suppliers, dealers or manufacturers for links and offer to write a review or testimonial of their products.
Branding through community participation
Encourage your users to make positive product reviews
Encourage your staff members to link to your site through their social media profiles or blogs/websites(if they have).
Sponsor or organize contests
Establish business-related link partnerships
Google Product Search Optimization