I have been using Adwords for a number of years and consider myself to be fairly knowledgeable with it. All of my ads to date have been directed at low profit margin items ($10-$20 per conversion) and I have therefore always abided by the general rule that I should go with only the narrowest possible search terms. However, I will soon be offering two items for sale with much higher profit margins ($350 and $550 per conversion respectively) and I am wondering whether I should consider broadening out my search terms in general and whether I should consider using broad search terms with appropriate negatives instead of limiting myself to only exact and phrase terms.
I understand that by broadening my search terms, I risk spending money on ads which may be less likely to turn into conversions, but if I keep my searches too narrow, I risk missing out on some high profit conversions.