S/he should be able to make you an expert in the field of art by providing you with knowledge (art historical, technical, financial etc..). As you are the one who has the final word on what goes in and what is left out of your collection, the more knowledgeable you are the better your collection will be. Your advisor will make sure that only the best works enter the collection. S/he will help you to evaluate the work and make sure you are achieving the best value for money. The advisor must at all times be able to give impartial, unbiased advice, must be trustworthy and transparent.