Does tolerance to alcohol affect blood/breath alcohol levels?
Typical roadside 'breath-testing' measures metabolites produced in the metabolism of alcohol (primarily, they measure ethanal, oxidised ethanol). The level measured level of intoxication therefore definitely differs from person to person, and even day-to-day for everyone. Some people have higher metabolic rates, and will metabolise the alochol faster. Some people have greater amounts of alcohol dehydrogenase (enzyme that breaks down alcohol) than others. It follows, that a larger person will likely be able to consume more alcohol compared to a smaller person (compare the concentration of 1 g of salt in a small glass, compared to a large glass)

However, there isn't really any fudge room for arguing against the tests. And most police-forces will back up breath testing with far more rigorous blood tests.