My apologies for answering in English, I wouldn't want to write in Japanese and accidentally explain something incorrectly.

出前営業 for businesses would mean traveling out to the customer in order to complete a sale or service.

If the customer calls a business and orders delivery, it would be normal "delivery service". Such as reference #2 for a Chinese restaurant.

However:
For appliances like air conditioners, there is time where the employee is working at the customer's location. In English, we would call a location where the work needs to be done a "work site". From that, we use the phrase "on-site" to describe the location.

Considering that this is for appliances, this could be either "on-site servicing" to describe employees traveling to the customer to complete work orders. It could also be considered "on-site sales" if they are visiting a customer for another reason and are able to sell additional products or services while they are visiting. (This could be an extended warranty, additional products in different rooms, etc.)

In reference #1, there is an example of the phrase being used in a situation where the business is offering a service where they will have employees come out to the customer and perform checks on their solar power meters and offer advice or services.

I heard that 出前営業 can be used to mean "trial" or "sample" in Japan; so this might be why there might be confusion. This would be different than either that or a normal delivery service like ordering food to be sent to your house.

Hopefully this helps answer your question, another term that might be worth looking into would be "upselling", which is an informal term in English that means to take advantage of chances to sell additional products.