I'd say both are important. Lower budget people would probably prefer a quicker cheaper less reliable test while higher budget people would prefer a more reliable and in depth test. I'm sure there will be cross over but my intuition is that maybe a third of each category would cross over, so by offering that alternative would expand your potential customer base by 40% using the previous assumption. Also, it'd be interesting if you could keep an anonymous database of any harmful results by area code with an easy interface on your website for people to search. You can add some call to action to get people to search their zip code and see what harmful substances were found in areas near them. This could lead to higher sales if there are negative results found. Maybe you can follow the same type of strategy where you ask them for their zip code and you can show them information of the risks in their area based off of scraped data from their municipal websites. I know my city has certain metrics that fail every few months, so providing information like this would be a great way to get them paranoid and want to follow up with a test from you.

Of course, the next logic step after the test, whether something harmful was found our not, is to send them information on items such as water filters from a company you partner with for affiliate advertising. Then for failed tests like mold or lead, you can send affiliate advertising material for lead and mold removal. Basically, send them to a page on your website with the same information as this pamphlet you sent them and on it you'll have affiliate links to earn extra money.