Purchase of gst 28% slab product

it will have no impact, since you have to collect the tax from customer the excess 10% that you are going to pay as input will be adjusted with your future tax liabilities arising due to addition of gross profit margin and other purchase related expenditure in addition to your costs of purchased products.

Can be done

The credit of GST paid at 28% now at time of purchase can be availed when the product is supplied to customer next month charging applicable output GST

 

good clarification and information