I think that it is good practice, as long as it is just a taste and not someone taking a bit of everything. If you are looking for a taste sampler I'd imagine that most pubs would charge you a fiver or something to try a few at a time. Set samplers are also a good way to try a few at a time and guarantee at least some money back to the bar. In my experience back in the states, most pubs that carry craft beer are willing to let you taste one or two for free if you seem to be generally interested-I'd assume that if you're a craft brew supplier then this is already built into your pricing since it is common practice.