There are hundreds of scales in the database related to the act of buying goods and services. Because there are so many, it is a challenge for researchers to find the one best suited for their purposes. Likewise, it is a challenge to limit this bundle to just the “best” 20. It was done by limiting this group to scales that are rather directly related to the act of purchase. Most prevalent in the bundle are different ways to measure purchase intention but several other facets of the activity are covered as well. To limit the size of this bundle, however, some important but distinctly different constructs are not included (search behavior, satisfaction, product usage, shopping orientations, and brand attitude). If enough interest is shown, bundles can be created for them in the future.
The Marketing Scales website is a gold mine of information. It is the only source that helps me understand the psychometric quality of the instruments used in past research. I recommend that researchers bookmark this site . . . they will be back!