S2 Technology interview questions

I received a message on LinkedIn, and Immediately they schedule the interview for L1, surprisingly level of the interview was very easy. on the same day, they schedule the L2 interview, again interview level was low. Here all fishy comes in my brain, generally German recruitment process takes a month or two for all these. but No client interview, No Glassdoor reviews, I got an offer without letterhead of company, No company history, a simple website where logos are copied paste from internet itself. I have not responded them back further.