diff --git a/stac_fastapi/pgstac/core.py b/stac_fastapi/pgstac/core.py
index d159ba6..59cecb9 100644
--- a/stac_fastapi/pgstac/core.py
+++ b/stac_fastapi/pgstac/core.py
@@ -88,12 +88,6 @@ async def all_collections(  # noqa: C901
                 **kwargs,
             )
 
-            # NOTE: `FreeTextExtension` - pgstac will only accept `str` so we need to
-            # join the list[str] with ` OR `
-            # ref: https://github.com/stac-utils/stac-fastapi-pgstac/pull/263
-            if q := clean_args.pop("q", None):
-                clean_args["q"] = " OR ".join(q) if isinstance(q, list) else q
-
             async with request.app.state.get_connection(request, "r") as conn:
                 q, p = render(
                     """
@@ -260,9 +254,11 @@ async def _search_base(  # noqa: C901
         search_request.conf = search_request.conf or {}
         search_request.conf["nohydrate"] = settings.use_api_hydrate
 
-        search_request_json = search_request.model_dump_json(
-            exclude_none=True, by_alias=True
+        search_request_json = search_request.model_dump(
+            exclude_none=True, by_alias=True, mode="json"
         )
+        search_request_json = self._clean_search_args({}, **search_request_json)
+        search_request_json = orjson.dumps(search_request_json)
 
         try:
             async with request.app.state.get_connection(request, "r") as conn:
@@ -613,10 +609,14 @@ def _clean_search_args(  # noqa: C901
                 else:
                     includes.add(field)
 
-            base_args["fields"] = {"include": includes, "exclude": excludes}
+            # ensure sets are converted to list to avoid JSON serialization issues
+            base_args["fields"] = {"include": list(includes), "exclude": list(excludes)}
 
         if q:
-            base_args["q"] = q
+            # NOTE: `FreeTextExtension` - pgstac will only accept `str` so we need to
+            # join the list[str] with ` OR `
+            # ref: https://github.com/stac-utils/stac-fastapi-pgstac/pull/263
+            base_args["q"] = " OR ".join(q) if isinstance(q, list) else q
 
         # Remove None values from dict
         clean = {}
diff --git a/tests/resources/test_item.py b/tests/resources/test_item.py
index 490d652..b4b009a 100644
--- a/tests/resources/test_item.py
+++ b/tests/resources/test_item.py
@@ -1701,15 +1701,64 @@ async def test_item_search_freetext(app_client, load_test_data, load_test_collec
         f"/collections/{test_item['collection']}/items", json=test_item
     )
     assert resp.status_code == 201
+    test_item2 = load_test_data("test_item2.json")
+    resp = await app_client.post(
+        f"/collections/{test_item['collection']}/items", json=test_item2
+    )
+    assert resp.status_code == 201
 
-    # free-text
-    resp = await app_client.get(
+    # free-text basic (using POST)
+    resp = await app_client.post(
         "/search",
-        params={"q": "orthorectified"},
+        json={"q": ["orthorectified"]},
+    )
+    assert resp.json()["numberReturned"] == 1
+    assert resp.json()["features"][0]["id"] == "test-item"
+
+    resp = await app_client.post(
+        "/search",
+        json={"q": ["orthorectified", "yo"]},
+    )
+    assert resp.json()["numberReturned"] == 1
+    assert resp.json()["features"][0]["id"] == "test-item"
+
+    resp = await app_client.post(
+        "/search",
+        json={"q": ["orthorectified", "Reflectance"]},
+    )
+    assert resp.json()["numberReturned"] == 2
+    assert resp.json()["features"][0]["id"] == "test-item"
+    assert resp.json()["features"][1]["id"] == "test-item2"
+
+    # free-text advanced (using POST)
+    resp = await app_client.post(
+        "/search",
+        json={"q": "orthorectified OR yo"},
     )
     assert resp.json()["numberReturned"] == 1
     assert resp.json()["features"][0]["id"] == "test-item"
 
+    resp = await app_client.post(
+        "/search",
+        json={"q": "orthorectified OR Reflectance"},
+    )
+    assert resp.json()["numberReturned"] == 2
+    assert resp.json()["features"][0]["id"] == "test-item"
+    assert resp.json()["features"][1]["id"] == "test-item2"
+
+    resp = await app_client.post(
+        "/search",
+        json={"q": "orthorectified AND Reflectance"},
+    )
+    assert resp.json()["numberReturned"] == 0
+
+    # free-text basic (using GET)
+    resp = await app_client.get(
+        "/search",
+        params={"q": "yo"},
+    )
+    assert resp.json()["numberReturned"] == 0
+
     resp = await app_client.get(
         "/search",
         params={"q": "orthorectified,yo"},
@@ -1717,6 +1766,22 @@ async def test_item_search_freetext(app_client, load_test_data, load_test_collec
     assert resp.json()["numberReturned"] == 1
     assert resp.json()["features"][0]["id"] == "test-item"
 
+    # free-text advanced (using GET)
+    resp = await app_client.get(
+        "/search",
+        params={"q": "orthorectified"},
+    )
+    assert resp.json()["numberReturned"] == 1
+    assert resp.json()["features"][0]["id"] == "test-item"
+
+    resp = await app_client.get(
+        "/search",
+        params={"q": "orthorectified OR Reflectance"},
+    )
+    assert resp.json()["numberReturned"] == 2
+    assert resp.json()["features"][0]["id"] == "test-item"
+    assert resp.json()["features"][1]["id"] == "test-item2"
+
     resp = await app_client.get(
         "/search",
         params={"q": "yo"},