What would you say about a customer who bought from you once, faced many problems with your product, and later he came back to buy again?

I will say, he is one of the three:

1. A customer who knows nothing

2. A customer who has no alternatives

3. A  LOYAL customer

With allot of optimism, I hope he is the last one.

.

It means either he is in serious need of that product and it's available anywhere else in the market or your product is still better than the others available. he could also be giving you a second chance so make sure to provide a better service this time.

Thank you very much to return

We hope to have our products have won the admiration

And regret for defects previous time

This is a good news that he came back.

It means he used to that company and even bad experience wasn't an obstacle to explore the market

He is having  a genuine demand for the product and his need/requirement is breaking all the drawbacks of the product that discourage him to buy it.

For necessities, nothing can stop to buy it.

This is a chance to improvise the product, with a detailed enquiry to make the customer more loyal to the product and also increase the market share of the product.

Sir I may be wrong but it could also be possible that I am a monopoly and the customer has no where else to go.

1. Giving your business a second chance
2. Your business is the only place that had the product
3. Cheaper than others
4. Faced more problems with other suppliers

You have generated enough faith in him and he came back with the expectation of an improved product/service.

OR

He may not have an alternate 

Bigger possibility that there is a problem with the customer not the product because the customer still buying it.

FULL AGREE WITH MR IBRAHIM