These are tough questions. It may be possible to hire third party marketing companies that would be able to do some testing for you to give you the metrics, but most likely the best option would be to do the testing in house. I think that you would need to set up a few of these alternative sampling methods and go out and do some A/B testing and see which have the highest ROI. It would be important to pick some metrics that you could use to measure that which would be uniform for each location so that there is no variance between what is being measured. For example if foot traffic to your booth is a goal then figuring out the best way to measure that or if actual sales is a goal that is much more easy because you can just weigh the cost of the event against the revenue generated at each location. Feel free to contact me for more in depth conversation about this. You can find me at gscsconsulting@gmail.com or at my website www.gscsconsulting.com