The idea sounds interesting initiailly until you think it out - the market is
already a mechanism to get local food to consumers - offering variety,
selection, competition, etc. The CSA-type benefits are not readily apparent,
except the idea of guaranteeing a certain volume of sales at the market for
participating farmers. It would be easier if farmers offered to sell vouvhers
at the beginning of the season that could be redeemed at their stall(s) - or
done market-wide - for produce. If there were a discount - say, $200 worth of
product for $175, it might attract customers. It's something akin the the
Farmers' Market Nutrition Program vouchers, which have been vital to
stabilizing many inner city markets in low-income areas. WHether this would
actually increase sales or income at a market depends on many factors - does
the farmer have additional product to sell; will the extra volume offset lower
prices; will it encourage customers to buy more than would usually; etc. etc.
I have heard of this done on a small scale, but nothing on a big scale.