Many people get the membership to increase sales but there are many perks with the membership that most don’t bother with. To sign up for the membership and then not bother with using the additional options, usually means that it probably will not work.
And as Atomicdiner says the more items you have the more likelihood of getting better results.

If you are not using social media ie pinterest (create boards with your items), twitter, facebook (create a business page with items going to your booth) or even sending your items to google shopping…having a membership will make little difference

(unless you go for the “big time memberships” which essentially means bonanza does pretty much all the work for you and sends out high priced ads)

I have a membership in this booth…mostly to be able to use some of the extra options…did my sales increase because I used the options, probably..since I was able to add Stripe as a payment option, use google analytics to monitor keywords, etc. Would they have increased by simply adding the membership but not using the extras, about the only thing it would have gotten me was some preference in search results…

but once Stripe becomes standard then I will probably drop the membership…

Increase your the number of listings, use social media, make sure you are in google shopping, and are compliant with google rules…do all of these before even considering a membership..

you are doing amazing work