Customer abilities and boosters can take effect at the same time, but they won't stack. For example:

1. Good Vibes: customers' patience can only recover to max patience
2. Fireproof: when used with Super Cooker, duration doesn't stack, but overlaps; effect lasts until whichever one's duration runs out last.
3. Cool Head: when used with puddings, duration doesn't stack, but overlaps; effect lasts until whichever one's duration runs out last.