Asking for a review is OK. Asking for a five-star review is not

I imagine that food truck operator would do a lot better by simply asking "Like or hate our food? Leave an honest review on <site> for a discount"

If their food and service is good, they'll get the positive reviews they need

I'd take that bet. There are so many people that will leave a 5 star review for a discount without thinking twice.

If the food and service is good what incentive is there to write a review at all? It's additional work and time for nothing. I never write positive reviews for that reason. For negative reviews it's completely opposite. So completely "honest" unedited review system would always skew very negative, because only negative reviewers have any incentive to write a review.

I was suggesting it as an alternative to offering a discount for 5-star reviews, just to offer a discount for honest reviews as it would likely generate the same result and the business would seem less shady to customers

There should be incentives in place to write a review.

I think even that is way over the line. Having to show the review means it's likely to drive the reviews up. I'd probably add a star or two because I'm afraid of conflict. And if the reviews give a discount, you encourage first time buyers to give a (made up) review before buying.

The only acceptable way to do it is "Please give us a review at [site]". No discounts or promotions.

True, having to show it definitely adds some social pressure to make it a good review. But it's still a little more ethical than explicitly asking for 5-star reviews

You're responding to someone that agrees with you. But also states that everyone else is review-farming and that if they don't do it they will be left behind.

I.e. your plan is doomed to fail.

I'm just stating that there's an alternative to asking for only 5-star reviews that will likely work better. Just asking for honest reviews (and offering a discount for them) is more ethical, and the honesty will be appreciated by customers.

And I agree with you that it's the right thing to do. But saying it will work better is probably not true.

Except maybe if you include a line like: "were not going to ask you for a 5 star review like others do, but reviews really make it break us and we're trying to be honest. Thanks for the support"