From a vendors view point having finance "deals" would be an excellent marketing tool.
All I owe is $42-00 at the local shop spent on fuel so I have hit my pay back limit

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I do this, ask how much am I prepared to spend each week on astronomy ($20 for me at the moment) put it away, and target your next big purchase, take from your savings cash for accessories. You become more careful about "little" purchases because that puts off the big purchase.
$20 is not much a week but that is one 12inch in 12 months or a top of the range 100mm apo in 5 years. If times are good you can add more dollars, dont buy that new t shirt and when home put the money you did not spend in a tin.
Keep emptying you tin into the savings account.
Still if presented with a credit option to buy more gear I unfortunately would probably talk myself into it

, certainly I would justify $20 per week repayments easily
alex