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.
I understand that by broadening my search terms, I risk spending money on ads which may be less likely to turn into conversions
That's not a problem as long as you're paying proportionately less for those searches.
Create some ad groups for the new products that are dedicated to the narrow search terms that you expect to do well. Make sure the ads are well customized for those searches.
Then also create separate ad groups for the broader searches that you'd like to test. Monitor your keyword query reports frequently, to watch for words that should be blocked, and also to watch for keyword gems that deserve special treatment.
Also, learn about modified broad match if you don't use it already.