score:7
Legally speaking, yes, you probably need a visa, since you are working in Singapore and getting paid for it.
In practice, since you're eligible for a 30-day visitor pass on arrival and this is a one-off, you'll be fine. In the unlikely event of being asked, you're visiting for "business meetings" and doing "sales demos" for a customer.
Source: Used to work for an IT company in Singapore that brought in people all the time for short pre-sales/integration/troubleshooting gigs very much like yours.