You will want to introduce your customers to as wide a range of your foods as possible and having tasting samples available is a good way to get their attention. Bear in mind that even though you may give samples away free of charge, the law sees this transaction as a sale, and their production and handling is still subject to legal control. Samples need to be protected from contamination such as undue handling, usually either from inquisitive pets or equally inquisitive children, so ensure samples are stored high up.
If your customers have to handle your food, try and make sure they don't touch other samples on the plate - cocktail sticks or tongs help to stop this. Most importantly, don't leave food that must be chilled for safety reasons out of chill control for long periods, so keep quantities to a minimum and throw out uneaten food if it has been out of refrigeration for a long time.
The law permits a maximum of four hours in most cases but it is best if high risk food is disposed of after one hour out of chill control. Bear in mind that for some foods, such as hard cheeses, temperature control is not critical to safety and longer periods are acceptable, so seek advice if in any doubt.
You may find your local market has its own conditions about food samples as this is at the discretion of the market organiser rather than any national legal requirement