Have a research about a certain company or you can have also the freedom to read the company's whitepaper firsthand. But having a whitepaper doesn't mean a company would more likely to be successfu.

if you mean a third party.. treat them like someone that walks passed you on the street.. would you seriously hand them your savingsincome without knowing them?

if your talking about a company. do due diligence. check out their company registration details then google map/streetview their address. make sure it does not lead to a po box/drop box/virtual mailbox address..

in short if you cant find enough information to slap them with a wet fish/court order should they do you wrong. dont trade with them.

even then be careful. after all butterfly labs had company registration details and an office, and product papers and business plans etc, yet they still ended up being scammy, same with MTGox

most people dont trust third parties/internet companies with anything more then the customer is willing to lose. most people only trade/spend amounts that can equate to some disposable income amount of a evening takeout meal, that wont hurt much if lost

I don't trust companies.
However I trust and have faith in certain individuals (developers, representatives) who have shown since many years that they want to progress Bitcoin together with the whole community, it's users and who are not just interested in personal profits like a few companies and their CEOs.

I do not really believe in this, they do not know me and I do not know him so I came when profitable and I went when it harmed me. I just believe in my god and family. besides that almost everything ever deceived me so i came if they give a profit

The trust in the crypto world is harder because transactions are irreversible, If you make it, there is no going back. It's better to do your home work about the company then try them. At this point, It's the same services that are popping up (exchanges or mixers etc.) so why use a new service in the first place If nothing better is offered such as low fees etc and If you are skeptical, just wait sometime and see reviews and feedback from users, It really doesn't worth risking your money.

I dont. Why would i ?

You didn't mentioned that which type of companies you are talking about. If you are referring to companies that owns altcoins, exchanges and wallets than it is quite hard to find out which company is trustworthy, so we have to go through some research about that company. I mostly check the legal entity of companies and their whitepaper, i also go through the reviews of the people working there or having any link with the company.

I don't trust the company easily. I try to do research about them, their scheme, their business growth, their historical background, their feed-backs and reviews about their business offers. I also verify their reputation in the market by personally visiting their office and meeting the company representative or executive officer and knowing about them in detail. I always prefer to seek help from my family members or my friends, rather than company's executive or other people to trust the company.

I don't!

of course trust is such a general word in my opinion. you can't just say you trust or don't trust someone. it has degrees. for example I trust the exchanges I use so much that I make a deposit and trade on their platform (for a time that I am trading) and I don't trust them at the same time that I withdraw when I am done trading or make a profit or want to stay away from the market....
the same goes for any other third party service that I use. we sometimes have to use them because we don't have any other choice but you always try and minimize the risks as much as you can.

Bitcoin market is too dangerous. You can't trust anyone blindfold due to anonymity of Bitcoins. Person may take your money in one moment and disappear the other moment.
So to trust websites, you must ascertain them on the scale of trustworthiness or credibility. Due to nonavailability of any regulating body, it is your personal understanding which could save you. Also it depends upon which type of website you using. If you using website which gives you specific pre-determined return, ignore it with all your senses as sooner or later, it will turn scam. IF you using exchanges and wallets, access them how trustworthy are they. Bitcointalk is great source of evaluation. Visit 'Service Announcement' section and you will get honest review on all websites.