Opensource content management systems like drupal, wordpress, etc. have modules for ecommerce which can probably be used for your purposes.
Please see a previous answer I posted here using drupal commerce, even though a bit old now.
Also, another system to check out is Opencart
I suggest you clarify the specific functionality you are looking for e.g.
- is it one vendor or multiple vendors?
- what payment methods will be made available? For instance, if multiple vendors, site may need to take commission out of payments...
- potential number of products/transactions per day
- hosted or self-hosted?
- how to handle shipping, freight, postage charges?
- and so on...
This will help narrow down which system to use.