It is definitely a race to the bottom, you could look up a case study on a company called tiny owl in India, they raised millions of dollars to compete in this space and their lesser funded competitor at the time, Swiggy.

Now Indias 2nd largest food delivery platform, this case study provides multiple insights,

1. Cheaper doesn't mean better even though it's an identical service

2. Even within zomato and swiggy there are extremely loyal users to each app not because of price but because of their ease of ordering, to each their own

3. There is no way you can compete with them on price, even after being funded and having scale on their side they still aren't profitable, zomato is valued at $5.4 billion

If you do have any ideas for a business, happy to discuss

Hey, I think the number one issue you're going to face is a factor of viability, to them you're a new website, not really well known and even if they give you the listing of the products, will you actually be able to generate interest and sales for them?

Once we understand this it would be much easier to tackle them in the following way

1. Ensure them a budget from your end on digital spend which will drive variable X amount of demand

2. They have nothing to lose, you aren't physically taking possession of their product unless it is actually rented out

3. To put it on the website you will need highly clarity images, which you could agree to share with them for their own social media

4. Use a couple of stock images, run some test campaigns and some them a basic real time demand on paper which would leave them calculating the potential revenue in their own head

These are just a few things, hope it helps!