not hating but imo i wouldnt use electrical tape. especially if u gotta unwrap it to diagnose a problem for any reason that stuff will get that wire sticker than a mo fo!! haha
heres an example of one i did (for my buddies toyota) solder + heatshrink + zipties
i assume shops use those connectors to cut time. it will take atleast 15 mins to solder up and heat shrink a harness if youre taking your time to make sure the soldering job is legit and not too much excess. i could see the shops crimping a harness up in 2 minutes. especially when they are trying to do a few cars in an hour. i never had any issues with the harness but if the buyer really thinks they are inferior i'll go ahead and solder up the harness if its a deal breaker.