The person that shows up with the $4000 bass and $4000 amp and knows no songs and fiddles with knobs all night to get his sound is going to either learn very fast or be pissed off at the "soul sucking" paying bands who insist that he learn the material they play. Notice I didn't specify cover band, etc. It's somewhat ironic to me though that the less a gig pays and the less busy a band is, the more the worry is on gear.
Show up prepared, on time, with gear that makes other peoples lives easier or doesn't add stress, you're a pro. No one will care how much your equipment cost as long as they don't need to worry about it. And no one will care how much your equipment cost if you can't play what is required either.
I know it seems like I mentioned money several times during this post. I love playing. I play in many different kinds of situations. It's not my only source of income, but the free gigs that are not free by choice are long gone. Professional anything means you are getting paid for your work, otherwise it is a hobby. Professional also means attitude, encompassing the preparedness, etc.
Oh, and for the record, I really enjoy wedding and corporate type gigs, soul sucking has to do more with attitude than material. One band I play with is tons of Motown, disco, soul, etc. and I love it. Another is lots of new dance music where I play along with sequences, and I love it. I can't say every song is my favorite, but I'm making money that provides for my family by playing music- tell me the part that sucks? I'm a social worker on the other Side of my life, and there is some pretty heavy stuff going on in the world. Covering "I Love it" along with a sequence is not even close to that!
Ok, off of my soapbox now! Have fun and do a good job; everything else tends to fall into place.