It's asking a lot for a vendor to have a complete "try something at no risk and return for any reason - we'll pay shipping both ways" policy, especially on something that will be evaluated as subjectively as a windscreen and where shipping costs are a fairly high percentage of the total cost. A few returns with this policy and you have to sell literally hundreds of non-returned products to simply break even. I, as s customer, don't want to pay a higher cost of goods for such a policy and don't expect such a policy.
In the end, the vendor is a business who can set their return policies as they see fit. These return policies are usually published and in full view to the customer prior to ordering., If the return policy isn't satisfactory to you, then don't order to begin with. Don't carp about it later.
BTW, almost any windscreen on a bike like the S10 will require some fiddling with the handguard, perches, and handlebar position to avoid hitting the screen at full lock. When you get a bigger windscreen, these problems are aggravated - nature of the beast. Some fiddling will usually find a compromise that works. Heck, it's quite possible to foul the tank on the stock bike with the handguards if you adjust the levers down a bit.
- Mark