Please check these sentences.

[razeen]

Some people buy roses at market, florist and supermarket.

Some people buy roses at markets, florists and supermarkets.

Some people buy roses at the market, florist and supermarket.

Some people buy roses at the market, the florist and the supermarket.

[knowable]

I would say:
Some people buy roses either at the market, florist or supermarket
Some people buy roses at the market, florist or supermarket.

But I am also thinking it should be ‘most people’ because it is at the market, florist or supermarket where you are (most) likely to find flowers for sale.