What are some good / the best reasons to trust Google's search engine's SERPs?

As i have previously answered on a similar question like this. My answer is. The biggest example that google will not do anything like that is wikipedia. There are a lot more examples like facebook,twitter etc. But i took wikipedia because of one important reason which i will explain in a short while. You all probably know about wikipedia. The most successful community maintained online information container. Well Google had something similar and that was knol. It is the short form of knowledge. It was a huge FAILURE. Still google never cared to destroy or down-rank wikipedia in any manner in their searches in order to help the knol. Hence It is well clear that google will never do such a thing.

I would say I agree with all the aforementioned answers. Google has lots to lose by manipulating the SERP's. And really no reason for it to manipulate the SERP as the big brands who can pay enough to temp Google for SERP manipulation already rank high enough for their specific niches. And for the smaller one’s well they can't tempt Google. Also time and again I have come across negative results about big names also ranking high on Google, like during the BP Oil crisis, most of BP's response pages were being featured in the PPC ads only. For SERP maximum results came from the pages with negative mention about BP and its crisis handling.. So it goes to show that Google does not shy away from showing thing as they are. And last but not the least, Google is constantly upgrading its algo to make the SERP more and more relevant and attuned to the internet user's needs. It has had some false starts but overall its concentrating hard on improving user experience. Majority of searches are conducted on Google only, so it obviously has people's preference and that wont come without the relevant search results showing and ranking.

I trust Google to provide relevant answers to my queries because it seems to deliver relevant answers to my queries.  I know that sounds a bit abtuse, but I have never examined "under the hood," so to speak, and don't have time to do so.  Like with the internal combustion engine connected to my automobile's drive shaft-- I don't care so much about how it turns the wheels, just that it delivers me to my destination with a minimum of problems and cost.

As for trust I trust that Google ethically indexes all sites the same. I do no always trust the people that manipulate the SERPS. Google stands to lose billions if they would do something like that

I trust them because every Google engineer I've spoken with has expressed the raison d'être of the company as "to index the world's information" and that's a powerful statement.