Founder Secondary Stock Sales: Experiences & Trusted Recommendations

Curious whether any founders here have completed a private secondary stock sale, particularly at the early-stage level?
I'm interested in hearing firsthand experiences and recommendations for reputable firms that work directly with founders to connect them with qualified secondary buyers.

Not looking for traditional fundraising platforms or investor-pool services. Specifically interested in firms that facilitate the purchase and transfer of existing founder-held shares.

If you've navigated this process or know a credible firm, I'd appreciate a recommendation or private introduction. Happy to connect directly.