What SKB said
I'm not sure where your friend researched! All over the internet there is a lot of info that says Syrians must always live alone - they are a solitary species. Dwarf hamsters can live in pairs but only if they are siblings and have always been together. Even then they can fight and need separating, and then you need two cages. It's usually recommended for a new or inexperienced owner to just get a single dwarf hamster too. With a pair the cage set up can be fiddly to avoid territorial behaviour and fighting. Or a single syrian!