Ask HN: How to sell Kleiner/Google-funded D-round Shares?

So I own a small number (under $100k at latest preferred valuation) of common shares in a very successful SaaS Analytics company that raised cumulatively close to $200mil from all the top investors. If you are in tech and in SV, chances are, your company uses its product. The company has been almost doubling its share price with every sale. And it has always had a healthy Revenue number to power up a big chunk of its growth.

I am currently in a rush to sell these shares. Unfortunately I am the only one former employee with such interest, so the volume is too small for secondary markets to take interest.

I've reached out to several professional liquidity solution companies, but received a low ball offer (price from a previous round). Maybe they expected that I would negotiate up and I missed the signal - regardless, it seems absurd to discount preferred shares at 40-50%. Especially for such a small volume. I mean, what do these guys know without access to company's finances, that Google did not when it invested $80 million (an had access to company's finances)?

So with that, what is you experience? How would you approach the sale of these shares?