There are two problems in buying from someone frum. The first is Lashon Harah. Similar to shidduchim, people are extremely relunctant to say anything bad about frum stores and businessmen. As a result how do you really know how trustworthy and reliable the dealer really is? I found this out the hard way. I bought replacement windowa from a frum guy. It took him months to do the job and he had my deposit. It turned out he was underfinanced and couldn’t get a line of credit. He was using new customer deposits to buy windows for previous customers.
The second problem refers to the first: bais din versus civil court