Question
It seems that support for a marketplace could be consider a competitive advantage if it's tightly integrated into the transaction, so should this be built in house, or use a 3rd party app to do this.
What do AirBNB, Fivver, Thumbtack use?
Answer
Honestly, UserVoice and Zendesk seem a little expensive
Fortunately, you can find alternatives like Kayako, which allow you to run your customer support department for only $15/month per agent, which is a bargain for everything you get:
Live chat + email + social media - unified channels support
Self-service center
Mobile SDK (Android + iOS)
Insightful reports
Team collaboration features
Assignment rules
Collision prevention
700+ app integrations thanks to Zapier.
You also get a Customer’s Journey, which allows you to visualize everything your customers have done and said, so you can bring context instantly and solve their issues ASAP.
Conclusion- There's no platform deemed to be 'Best' choose what suits you.
I hope that helps!
