Having spent 5 years on the Stock Exchange analysing how other people had successfully exploited business opportunities he decided to become actively involved in business and swapped managing millions for investors for the opportunity to grow the family jewellery business. He invested his money from London and started learning the business from the bottom up (starting with learning how to fit batteries and straps to watches!).

He set about re-skilling himself for the new challenge by taking the National Association of Goldsmiths Diploma in the Distinction grade, achieving the second highest result in Ireland.

While running the Cornelscourt outlet (www.costellojewellers.ie) he started Ireland’s first ever Scrap Gold Week in aid of St. Vincent de Paul. He was president of the national youth forum of SVdP in 1997. He also established Student Of The Year Awards in 14 of the area's schools.

Industrial disputes at Dunnes Stores caused serious difficulties for the business resulting in it remaining closed for a period of time due to picketing of Dunnes by staff.

As a result of a robbery at the Bray outlet of Costello Jewellers he started a campaign to have CCTV installed in his home town of Bray, Co. Wicklow.
The successful campaign involved conducting a survey of Bray residents and a concerted campaign of raising the issue with the local media. A comprehensive document supporting the case for the immediate introduction of CCTV was prepared by Eoin for presentation to the Bray Urban District Council. The campaign came to a successful conclusion in 2000 with the provision of CCTV in Bray.

In 1999 he took the momentous decision to sell his physical business to invest in internet start-up Novara.ie.