Please go. Like the others have said, let the host know in advance that you are not intending on buying. If it is a friend, she shouldn't care. They (consultants) count on hooking you into getting 'something' once you are there to see how wonderful their products are. Also, many times the host will get a little something extra for X number of people attending. Stay strong and just say no. I already know you will....Dave's Snowball is a great motivator!
BTW: I have been on all three sides of this scenario (consultant, host, party-goer that doesn't buy) and at no time in any of these rolls did I feel anything was wrong with it. Have fun!! :)
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***EDIT***
When I was a consultant, the products I showed were my own. I did not need to buy samples for trials (like Mary Kay parties). I did however have to buy the pamphlets, catalogues, receipts, future host incentives (to get guests to book a party), and door prizes. I also gave a gift to anyone that was invited that brought another person. These things came out of my own pocket, and I certainly did not go into business to lose money. I did not care if people came or not but the more the merrier even if sales were low. Just don't take anything with you. (Some parties with low attendance had higher sales than bigger parties, so you just never know.)
That said, I agree with these suggestions:
~ don't take a catalog unless you plan to buy
~ don't invite yourself if you don't plan to buy
~ do bring a friend (if you are invited to do so - most consultants encourage this - maybe she will buy something)
...and if you don't want any followup calls or emails, simply don't fill out anything with your information (drawing slips, surveys, etc)