It does not make a difference between selling a company or a small store, it differs according to the value and how to prove that scam does not occur.

Selling websites is considered relatively safe, so you can find a lot of people who can guarantee the amount.

If the amount you intend to get from this deal is not large, you can use these options:

Bitify.com:
Bitcointalk escrow members:
Bitrated:

If your crypto currency has good profits, high revenue,  lots of clients  and so on brokers will come to you trying to buy your company. Maybe even competitors may try to do that.

What kind of company are you talking about? A casino, a mixer? I think those are the most common success in cryptocurrency industry so far.

There are also many crypto companies which are outright scams and ponzi schemes. Those companies are just illegal and have no value.