From Longman Dictionary of Contemporary Englishbuy into something phrasal verb1 informalBELIEVE to accept that an idea is right and allow it to influence you I never bought into this idea that you have to be thin to be attractive.2 BUYto buy part of a business or organization, especially because you want to control it Investors were invited to buy into state-owned enterprises. → buy→ See Verb table
Examples from the Corpus
buy into • Softbank claims that it is better at picking winners and that it is buying into a growth industry.• Check out the prices for buying into a hamburger or a pizza chain.• It has never been clear to what extent Gore buys into any of this.• Perhaps Hathaway was naive to buy into his dream of a record for their 7-year - old daughter.• He did not buy into hyped investments.• Some people are on the outside of all that, wishing they could buy into it.• The media buy into the scam because such scare stories about unseen threats make good headlines.From Longman Business Dictionarybuy into something phrasal verb [transitive]1COMMERCEto buy part of a company or businessA lot of US companies are buying into Japanese firms.2FINANCEto invest in somethingIn momentum investing, the name of the game is being the first investor to buy into a stock, and the first investor to sell out before bad news breaks.3to believe in something completelyMy last employer expected us to buy into the ideas of every new American business guru, without question. → buy→ See Verb table 