Interesting twist of the mindset to prevent yourself from being guilt-tripped into buying something you hardly need/want.
From Robert Cialdini's Influence book.
Door-to-door fire-alarm companies will frequently use this approach. Typically, their product, while effective enough, will be overpriced. Trusting that you will not be familiar with the retail costs of such a system and that, if you decide to buy one, you will feel obligated to the company that provided with a free extinguisher and home inspection, these companies will pressure you for an immediate sale.
Using this free-information-and-inspection gambit, fire-protection sales organizations have flourished around the country.
If you were to find yourself in such a situation with the realisation that the primary motive of the inspector's visit was to sell you a costly alarm system, your most effective next action would be a simple, private maneuver.
It would involve the mental act of redefinition.
Merely define whatever you have received from the inspector - extinguisher, safety information, hazard inspection - not as gifts, but as sales devices, and you will be free to decline (or accept) his purchase offer without even a tug of the reciprocity rule: a favor rightly follows a favor - not a piece of sales strategy. And if he subsequently responds to your refusal by proposing that you, at least, give him the names of some friends he might call on, use your mental maneuver on him again. Define his retreat to this smaller request as what you recognise it to be - a compliance tactic. Once done, there would be no pressure to offer the names as a return concession, since his reduced request would not be viewed as a real concession.
At this point, un-hampered by an inappropriately triggered sense of obligation, you may once again be as complaint or noncomplaint as you wish.
Provided you are so inclined, you might even turn his own weapon of influence against him. Recall that the rule of reciprocation entitles a person who has acted in a certain way to a dose of the same thing. If you have determined that the fire inspector's gifts were used, not as genuine gifts, but to make a profit from you, then you might want to use them to make a profit of your own.
Simply take whatever the inspector is willing to provide - safety information, home extinguisher - thank him politely, and show him out the door.
After all, the reciprocity rule asserts that if justice is to be done, exploitation attempts should be exploited.