I run a business in a related industry, its payment on receipt of invoice, most pay same day some a few days later. The system is completely digital, the quotes explicitly state payment terms and deposits. Yet some dawdle with payment.
www.gov.uk/invoicing-and-taking-payment-from-customers/payment-obligations
'You can set your own payment terms, such as discounts for early payment and payment upfront.
Unless you agree on a payment date, the customer must pay you within 30 days of getting your invoice or the goods or service'.
One of the issues is not working capital, it's the speed of the work, by the end of the week this can add up. I audit every week, paying the same day cuts the accounting work. I don't want to be chasing monies the week after, same day means updating the sale, cost, and the overall finances, that day is closed once all monies are in.
Profits are usually £7-10 thousand per month, so money is NOT the issue.
Incidentally whilst managing at a £10 million turnover company, £350,000 was outstanding at any one time due to slow payers, that was a purely domestic company.
What's annoying is this work is quoted, and booked in, so the customer knows you're coming yet they've not prepared payment. So the upshot of this is these customers despite being on friendly terms, refuse to work for them again.
On another note, I've just had to pay upfront for dental work. In another industry, I worked, when we booked DJs we had to pay thousands upfront or pay when they'd finished the set, so they could move on to their next booking.