If you doubt me, ask me any question about them, any implementation detail, I can explain it to you. I can discuss parsers, stack frame optimization and calling conventions for days, weird edge cases in the C syntax, trigraphs, whatever; I can tell you not only how to implement a search engine index in minute detail, methods for compressing a lexicon, but how to implement a crawler, how to extract keywords from a website, how to identify the language of a website, we can discuss ranking algorithms, we can discuss absurd number of different ways a web server may tell you which character encoding a page has, I can tell you why some websites have the DTD "-//SoftQuad Software//DTD HoTMetaL PRO 6.0::19990601::extensions to HTML 4.0//EN", we can discuss the absurdly inconsistent usage of the lang tag, we can talk about how sequential writes sometimes are still faster on SSDs, we can talk about how to make a SQL query perform well on a table with half a billion rows, we can talk about blackhat SEO, we can talk about how to implement a hash table on disk and when that is and isn't a good idea, we can discuss B-trees.
I also have the finished product to show. It's not open source, but if all this fails to convince you, I can bring my laptop and we can walk through the actual code.
If all of this is bullshit, I'm the greatest bullshit-artist alive, and you can just put me in sales instead.