I didn't get a chance to do my Windex experiment...so I'll contribute in the boring way!
I just had a job from someone I do a lot of work with - This is my "Side business", not my normal "Real" job. Printing 2 full rolls of banners, going to about 40 different schools. The art is supplied - so I just print, trim, hem pole pockets into it, and kit it for each school with some decals / posters, etc. Pretty big job, while working another 8 hour job anyways - Worth about $2500, and I do it in the night after my day job...so it's about 3-4 days of work, few hours a day so I dont kill myself.
Well, on Day 3.... after staring at these damn banners for hours and hours... I notice when she setup the artwork adding the school names in... she moved the vector, and it wasn't grouped - So theres a big piece of the wing where it shouldn't be. This has gone through a bunch of vendors - 1000 posters were made, some coasters, flyers, every single school signed off on the proof... no one noticed it. I go and point it out to her...And ask if its supposed to be that way... to which I know it's not, but I didn't want to sound like a know it all. She's so stressed... because its on her, and everything has to be re-done.
I know if I charge her the full price to re-do it all, she makes zero profit on the job...so I offer to do it for material / ink cost.... about $500. She's extremely happy... because she has 3 other vendors she has to pay to get everything re-done as well - turns out every single vendor re-printed it for a discount, and apologized for not seeing it before printing it, even though it was her artwork.
It's 100% her fault - Everyone of us could have been dicks and re-charged full price - but you need to keep your customers happy and work with them. Here I am at 3 in the morning cutting up and putting pole pockets in banners to help a customer in a jam, and making no profit on it.
Using the wrong material for the job, no matter the reason - or doing a shitty job, and not wanting to fix it because you'll be out some money is a good way to lose customers. I probably shouldnt have been so forgiving since it's not my mistake at all - but I take pride in my work... I convinced her to re-print everything VS sending it out and hoping no one notices... because I didn't want to put out a bunch of shoddy artwork, whether it was my mistake or not.
Don't try to make excuses - I can wrap vehicles pretty easy... but I dont have space to do it properly at my house - I could do it in my drive way and get away with a bunch of dust under the wrap... but I don't - If you can't do a job right... you shouldn't try to do it. Focus on what you can do, and can do well - Otherwise word will get out about the crappy work you do... and being in a small town / island... no one will want to work with you. 1/10 customers who are happy with your work will leave a review, or sing your praises - 9/10 customers who are unhappy with your work will do the same.... And that word travels faster and further.
You can buy most vinyl by the Ft - Black ,white, buy 10-20 FT of the popular colors - Store it at home under your bed if you have to.