What’s the most universally appealing service?

Might sound like a weird question, but allow me to elaborate. I think some of you fine folk here on BHW will be able to help me, and I thank you in advance for that.

I have a sales background, and I’m very good at getting people interested. Prospecting and getting prospective clients on the phone isn’t an issue, but I simply don’t know what service to sell. I’m targeting local businesses (think restaurants, contractors, etc).

I plan on using upwork for fulfillment, just want to get the opinions of those here on BHW

thanks!