Usually they have someone make a purchase from the seller in such a situation, to confirm the information they have received from the tipster. Then they take the tip, along with the purchase, and present it to a magistrate to obtain a warrant.
It could be. In addition to the police, the manufacturer of the handbags, tec., may be able to get a search warrant as well. Generally, police must be able to establish that there is probable cause that the search would result in the seizure of evidence of a crime. A tip is generally not enough unless the tipster had given information to the police in the past which proved to be true. Otherwise, the police will have to satisfy a judge that there is other evidence supporting the tip. Lawyers call this corroboration. Judges generally (again) want a little more assurance for a search warrant for a private home then a warrant for a business or storage facility.
The police may be able to get corroboration in a number of ways. For example, they could watch the house to see if people are coming and going in the manner of a business or whether boxes are being delivered or taken out of the house. They also may ask the post office for information about your mail. They need a warrant to open mail, which also requires probable cause, but the postal inspectors can read the outside of the mail and provide a list of the return addresses to the police. They also may ask other delivery services for information. The police may also ask the tipster for the name of someone else who purchased items from the house. A second tipster may also be corroboration.
Probably, the favorite means of corroboration would be to have the tipster place a call to the seller to discuss buying more items. In many states, the police may record such calls without a warrant if the caller consents. Of course, they will have no trouble getting consent since the caller is the tipster. Alternatively, a police officer could place the call on the pretext that she or he is a friend of the tipster.
The police may get corroboration from evidence of anti-surveillance techniques, that is, taking steps to avoid detection such as stopping mail, obtaining a mailbox off site, refusing to take calls from the tipster, etc. The key is whether the police can convince the judge that the homeowner is doing these things to avoid detection.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.
You didn't provide enough facts to give a complete answer. Please also allow me to emphasize that it is important that you contact an experienced criminal attorney in your area to discuss your situation. But generally speaking, the Fourth Amendment provides that probable cause is the standard of proof required for a police officer to obtain a warrant. If a mere "tipster" provides an anonymous tip concerning a potential violation, then the majority of jurisdictions would generally require the police to somehow independently verify the information. But again, every fact situation is different, so it is important that you seek legal counsel in your area.