I don't know what consumer law is but if everything goes wrong what are my rights?
In Taiwan, what the law says and what actually happens are two different things.
If this is a brand-new scooter, most reputable dealers will honour the guarantee. Just politely discuss the issues at hand and (most likely) they'll get things sorted out for you. Ranting and shouting will usually not have the desired effect, unless you're out of other options.
If it's secondhand ... well, I suggest you start reading some books about fixing scooters.