It is absolutely vital that you believe in the products or services your clients ask you to help them sell. You must ‘eat the dogfood’.
I did a project for a credit card company. I didn’t have much experience with them, so I took out a credit card with their company.
A sports drink company wanted us to help them re-brand. I drank an awful lot of their drinks.
A sunglasses company wants a video- guess what? I bought a pair to try out. On my own dime.
If a client is trusting you to market their product, you absolutely MUST find a personal connection to their product. You need to use it. You need to believe in it. Otherwise, you’re a liar and the work will suck.