I am looking for a specilist to advise me to build a good site. The idea is to help me to follow properly a team do a good work (build a good site in Magento concerning the design and programming)
My best advice is to go to https://magento.com/ and have a look through the "partner" area. You need to find a partner that aligns with you needs - I would talk with a few. Also asking in the more general forums area might help where some of the partners hang out. I am not going to recommend one partner over another in this area.
