Adding bonus gifts to orders is a way to build up customer loyalty.
Done right, the customer can feel like you're over-delivering value and there's a touch of surprise.
Deciding when to add bonus gifts can get complicated through.
The simple decision is every time. If your bonuses are inexpensive and you have enough to vary them, just add them. Even if you have to do a little bit of product development to create a low-cost order bonus, it could pay off.
The more complex decision would be to look at your metrics:
- How many times does an average customer order? (measured by Average Orders per Customer in my app)
- How long do customers wait in-between orders? (measured by Average Latency)
- What percentage of each order's profit is taken away from free bonuses?
- Is this order special in any way? e.g. First order, 10th order, larger size than usual, etc
If you have the order volume, you could do a holdout test. That's where you mail some customers the bonuses while "holding back" the bonuses from other customers. Then compare if the bonuses were effective.