It is inevitable that at some point you will make a mistake on a customer's order and have a choice; fix the issue and save the customer or dig in your heels and lose that customer. What some decorators (especially newer ones) may miss is that this may be more of an opportunity than anything else. It may cost you a little bit on the front end but fixing a problem can often turn out to be lucrative in the long run. Your customer may have much more buying power than you are aware or be well connected with potential referrals. It also speaks a lot to your integrity, ability to adapt, be agile and show you actually care. Just imagine you are the customer and how you would feel. The best case is to avoid a mistake in the first place.
Here are some things to help in that area:
Remember if an issue does come up let your customer have their say and explain their position and no matter who is at fault do your best to rectify the situation. This might mean a full redo of the order at no-cost, partial credit or credit towards a future order.