Recent hires have included Ian Woodward from closed Knutsford saleroom Wright Marshall and jewellery specialist Helena Waudby from Peter Wilson in Nantwich.
Two new trainee valuers have also been taken on: Elizabeth Oliver and Simon Grover. The new staff are managed by Ashley Jones who joined in 2015.
The auction house now has nine full-time and 12 part-time staff.
Trevanion said: “The arrival of our new members strengthens and expands our existing cataloguing and auctioneering team.”
Trevanion and Dean met studying fine art valuation at Southampton University and after pursuing separate careers they teamed up to open their firm in Whitchurch, Shropshire in 2014.
Dean has now re-located to the north-west of England and added: “I have had a wonderful four years… and it is now time for me to move on.”