Do potenial customers frown upon dogs being in the crate if you step out?

It depends on the owner and what you've discussed ahead of time. Many owners use crates at home, and they would likely expect some continuity with their home rules. Likewise, for dogs who are not crated at home, owners may prefer that they are also not crated while at the sitter's. Many are also flexible; they may have dogs who are crate trained, but not frequently crated at home, and they leave it at your discretion whether or not to use the crate. I have many clients who don't use crates at all, and a few who always use them. My own dogs are crated depending on the situation; they both love the crate and spend a good portion of the day sleeping in there willingly. Most of the time they are completely trustworthy when I leave, but for whatever reason, my border collie mix hates it when I go to work, so to prevent what my walker calls "dog parties" (and what I call "really, Carys?? AGAIN??"), she has to be crated until the walker comes by to take them out. Point is - every owner has different wants and needs from a sitter.

Just outline what your own house rules are on your profile, and discuss crating (including the amount of time dogs are crated) with potential clients at the meet and greet. It doesn't hurt to explain your reasoning. Also, if you require crates, be sure to have an alternative method in place in case you end up with a dog who is not actually crate trained, like a dog-proofed bathroom, gated hallway, or playpen. Some dogs will get stressed enough in the crate to seriously injure themselves trying to escape.

Hi Angela,
If you require all your pet guests to be crate trained make sure you state that in your profile. When you have the interview with the potential customer, re-state it and make sure they understand and explain that if/when you have to leave the home for (hour/etc), for the SAFETY of all your pet guests they must be crated. When it comes to the safety of their furry family member they understand. Not all owners have crate trained dogs.

If you do decided to take a dog that isn't crate trained, you can close them in the bathroom. Just make sure everything is out of reach -including the waste basket- and cabinets are secure. I pet sit a dog that knows how to open the bottom cabinet doors. He only does that when he wants me to get up at 4:30 a.m. The bathroom door stays open so he goes in there when his nudging and kisses don't work. Good Luck and Enjoy!

Some might, but I require dogs to have some crate training before they stay with me. If the owner doesn't like that, they are free to choose another sitter.
If you mean, "do enough owners hate it that it would hurt my business?", I'd say no, not at all. Most are understanding when I explain that I do it for their dog's safety.

All customers do not act the same or have the same expectations. It all depends on what you have been advertising as your pet-sitting environment. You should include that information in your profile that dogs will be crated when you are not home, plus you should give the client an idea of how longer on average you may be away. When you are contacted by clients, you need to discuss this because not all dogs are used to be crated. You should find out each dog's situation before taking on clients.

In my case, dogs have the run of one floor. If I feel I need to keep them apart, I can do so with baby gates. Some clients have brought over their own crates, but I do not supply them and don't even own one. During my M&Gs, I do let clients know that while I am at home most of the time, I may go out to run errands or have other commitments, and it would typically be for less than three hours.